Extend lub/glb to more types

[ggreif]

This is a peek at the final version and request for comment on the further direction.

Added to the type algebra:

• tuples
• objects
• arrays
• functions
• Shared
• futures

Laundry list:

• test glb for variants
• remove TBR?
• consider var in objects, arrays (do they add indeterminism/effects?)
• are there any other meaningful points in the lattice?
• move the clause(s) t1', t2' when eq t1' t2' -> t1 further up? Costly
• alpha-equivalence in polymorphic function types, need to open
• go contravariantly with Func type param bounds
• can we relax sharing (resp. control) mode checking for functions?
• style issue: make the use of t1' etc. consistent in touched functions
• recursion in types
• make is_recursive_con more precise Not needed any more
• @glb (Int, Nat)/2 appears in types, sometimes we need to reduce!
• check whether we need to observe polarity for bounded params