Add Profile.callers to determine main callers of a particular function

[timholy]

EDIT: name changed to "callers"

This is somewhat like the Profiling analog of @which. It's quite useful in aggregating results from a complex sequence of runs.

Demo: in Gadfly/test,

julia> @profile include("test.jl")

julia> Profile.whocalled("cyclezip")
3-element Array{(Any,Any),1}:
 (392,LineInfo("circle","/home/tim/.julia/v0.3/Compose/src/form.jl",139,false))
 (214,LineInfo("text","/home/tim/.julia/v0.3/Compose/src/form.jl",249,false))  
 (3,LineInfo("rectangle","/home/tim/.julia/v0.3/Compose/src/form.jl",93,false))

[timholy]

EDIT: since this is retrospective, I changed the name from whocalls to whocalled. Compared to the original implementation, I also switched over to a keyword interface for more detailed match information, added the ability to specify a line range, and switched the order of the outputs. I edited the post above to match the new style.

I'm inclined to merge this, so let me know if this should wait for 0.4.

[quinnj]

I was actually thinking the other night that something like this would be really useful. +1

[catawbasam]

+1

[timholy]

Thanks for the interest. I'll merge this once 0.4 development starts.

[timholy]

Given the "whorequires" -> "dependents" renaming in #7924, I'll give one last chance for commenting on this name.

[IainNZ]

Profile.callers() ?

[timholy]

I like it. I'll change it barring other suggestions.

[staticfloat]

I like .callers().