rename test->isprefabkey
Merge branch 'master' of https://github.com/samth/pycket
Merge branch 'master' of https://github.com/samth/pycket
Merge branch 'master' of https://github.com/samth/pycket
Add nucleic2 which is problematic for branches.
fix off by one error in the (so far unused) depth_and_size
simplify the env pruning code

get rid of the -1 special case and just always use the precise number of
envs to remove.
a test for remove_num_envs
more aggressive pruning

also prune the environment in a Let when some of the rhs expressions
don't need the full enclosing environment.
fix translation
Merge branch 'master' of https://github.com/samth/pycket
fix translation
Add a prim needed for mpair benchmarks.
Merge branch 'master' into loop-detection
Merge branch 'master' of https://github.com/samth/pycket
add unsafe-fx<= and unsafe-fx>=
Merge branch 'master' into loop-detection