Strategies for Cells

[samth]

Right now fixnums in set!'ed variables always requires allocation. This makes me sad.

[cfbolz]

The types that we see in test_larger.py:

None: 126
W_Fixnum: 145
W_Null: 3
W_Prim: 7
W_Closure: 118

For W_Fixnum we should use a strategy, for the W_Closure case maybe we can extend when RecLambda is used a bit.

[cfbolz]

Here's the diff to do this type profiling (untranslated):

https://gist.github.com/cfbolz/7799bba1031ef2e3f13d

Current numbers for all tests:

at construction
W_Null: 2
W_Fixnum: 41
None: 28

when set
W_MCons: 2
W_ClosureSize1: 7
W_PromotableClosure: 1
W_Fixnum: 139
W_Bool: 2

This means fixnum strategies are still a good idea, and the reclambda removal is very successful