Fix multiple problems with views-of-views

Due to what was probably a copy/paste error, the tests
were grabbing a global variable A (rather than an argument)
that happened to be a plain array. So we weren't really testing
views-of-views.

Unsurprisingly, fixing this problem uncovered bugs.
Many "simple" things worked, but sufficiently complicated
constructs like
   A = rand(20, 20, 20)
   B = slice(A, 1:5, 6, 6:9)
   C = sub(B, :)
(specifically, those that use linear indexing in creation
of a view-of-view) certainly had problems.

Drat. Well, hopefully this has been rare up until now;
it seems rather likely that folks would have gotten BoundsErrors if
anyone had actually been using this. But we start returning views from
getindex it will become common, so better that it was caught now.

In debugging and fixing the problems, I took the opportunity to
do some cleanup to make this more maintainable, specifically:
adopting a consistent naming convention, improving many variable
names, and adding comments.

base/multidimensional.jl

@@ -345,61 +345,71 @@ end
 # the corresponding cartesian index into the parent, and then uses
 # dims to convert back to a linear index into the parent array.
 #
-# However, a common case is linindex::UnitRange.
-# Since div is slow and in(j::Int, linindex::UnitRange) is fast,
+# However, a common case is linindex::Range.
+# Since div is slow and in(j::Int, linindex::Range) is fast,
 # it can be much faster to generate all possibilities and
 # then test whether the corresponding linear index is in linindex.
 # One exception occurs when only a small subset of the total
 # is desired, in which case we fall back to the div-based algorithm.
-stagedfunction merge_indexes(V, indexes::NTuple, dims::Dims, linindex::UnitRange{Int})
-    N = length(indexes)
+#stagedfunction merge_indexes{T<:Integer}(V, parentindexes::NTuple, parentdims::Dims, linindex::Union(Colon,Range{T}), lindim)
+stagedfunction merge_indexes_in{TT}(V, parentindexes::TT, parentdims::Dims, linindex, lindim)
+    N = length(parentindexes)   # number of parent axes we're merging
     N > 0 || throw(ArgumentError("cannot merge empty indexes"))
+    lengthexpr = linindex == Colon ? (:(prod(size(V)[lindim:end]))) : (:(length(linindex)))
+    L = symbol(string("Istride_", N+1))  # length of V's trailing dimensions
     quote
-        n = length(linindex)
-        Base.Cartesian.@nexprs $N d->(I_d = indexes[d])
-        L = 1
-        dimoffset = ndims(V.parent) - length(dims)
-        Base.Cartesian.@nexprs $N d->(L *= dimsize(V.parent, d+dimoffset, I_d))
-        if n < 0.1L   # this has not been carefully tuned
-            return merge_indexes_div(V, indexes, dims, linindex)
+        n = $lengthexpr
+        Base.Cartesian.@nexprs $N d->(I_d = parentindexes[d])
+        pdimoffset = ndims(V.parent) - length(parentdims)
+        Istride_1 = 1   # parentindexes strides
+        Base.Cartesian.@nexprs $N d->(Istride_{d+1} = Istride_d*dimsize(V.parent, d+pdimoffset, I_d))
+        Istridet = Base.Cartesian.@ntuple $(N+1) d->Istride_d
+        if n < 0.1*$L   # this has not been carefully tuned
+            return merge_indexes_div(V, parentindexes, parentdims, linindex, lindim)
         end
         Pstride_1 = 1   # parent strides
-        Base.Cartesian.@nexprs $(N-1) d->(Pstride_{d+1} = Pstride_d*dims[d])
-        Istride_1 = 1   # indexes strides
-        Base.Cartesian.@nexprs $(N-1) d->(Istride_{d+1} = Istride_d*dimsize(V, d+dimoffset, I_d))
-        Base.Cartesian.@nexprs $N d->(counter_d = 1) # counter_0 is a linear index into indexes
+        Base.Cartesian.@nexprs $(N-1) d->(Pstride_{d+1} = Pstride_d*parentdims[d])
+        Base.Cartesian.@nexprs $N d->(counter_d = 1) # counter_0 is a linear index into parentindexes
         Base.Cartesian.@nexprs $N d->(offset_d = 1)  # offset_0 is a linear index into parent
         k = 0
         index = Array(Int, n)
-        Base.Cartesian.@nloops $N i d->(1:dimsize(V, d+dimoffset, I_d)) d->(offset_{d-1} = offset_d + (I_d[i_d]-1)*Pstride_d; counter_{d-1} = counter_d + (i_d-1)*Istride_d) begin
+        Base.Cartesian.@nloops $N i d->(1:dimsize(V.parent, d+pdimoffset, I_d)) d->(offset_{d-1} = offset_d + (I_d[i_d]-1)*Pstride_d; counter_{d-1} = counter_d + (i_d-1)*Istride_d) begin
             if in(counter_0, linindex)
                 index[k+=1] = offset_0
             end
         end
         index
     end
 end
-merge_indexes(V, indexes::NTuple, dims::Dims, linindex) = merge_indexes_div(V, indexes, dims, linindex)
+
+# HACK: dispatch seemingly wasn't working properly
+function merge_indexes(V, parentindexes::NTuple, parentdims::Dims, linindex, lindim)
+    if isa(linindex, Colon) || isa(linindex, Range)
+        return merge_indexes_in(V, parentindexes, parentdims, linindex, lindim)
+    end
+    merge_indexes_div(V, parentindexes, parentdims, linindex, lindim)
+end
 
 # This could be written as a regular function, but performance
 # will be better using Cartesian macros to avoid the heap and
 # an extra loop.
-stagedfunction merge_indexes_div(V, indexes::NTuple, dims::Dims, linindex)
-    N = length(indexes)
+stagedfunction merge_indexes_div{TT}(V, parentindexes::TT, parentdims::Dims, linindex, lindim)
+    N = length(parentindexes)
     N > 0 || throw(ArgumentError("cannot merge empty indexes"))
     Istride_N = symbol("Istride_$N")
+    lengthexpr = :(length(linindex))
     quote
-        Base.Cartesian.@nexprs $N d->(I_d = indexes[d])
+        Base.Cartesian.@nexprs $N d->(I_d = parentindexes[d])
         Pstride_1 = 1   # parent strides
-        Base.Cartesian.@nexprs $(N-1) d->(Pstride_{d+1} = Pstride_d*dims[d])
-        Istride_1 = 1   # indexes strides
-        dimoffset = ndims(V.parent) - length(dims)
-        Base.Cartesian.@nexprs $(N-1) d->(Istride_{d+1} = Istride_d*dimsize(V.parent, d+dimoffset, I_d))
-        n = length(linindex)
-        L = $(Istride_N) * dimsize(V.parent, $N+dimoffset, indexes[end])
+        Base.Cartesian.@nexprs $(N-1) d->(Pstride_{d+1} = Pstride_d*parentdims[d])
+        Istride_1 = 1   # parentindexes strides
+        pdimoffset = ndims(V.parent) - length(parentdims)
+        Base.Cartesian.@nexprs $(N-1) d->(Istride_{d+1} = Istride_d*dimsize(V.parent, d+pdimoffset, I_d))
+        n = $lengthexpr
+        L = $(Istride_N) * dimsize(V.parent, $N+pdimoffset, parentindexes[end])
         index = Array(Int, n)
         for i = 1:n
-            k = linindex[i] # k is the indexes-centered linear index
+            k = linindex[i] # k is the parentindexes-centered linear index
             1 <= k <= L || throw(BoundsError())
             k -= 1
             j = 0  # j will be the new parent-centered linear index