Expanding TS optional arguments into overloads.

  - Fixed most of prelude as well.
Merge pull request #64 from UCSD-PL/expand_opt_args

Expanding TS optional arguments into overloads.
asd
fixing error in spec for Array.reduce in prelude
hopefully final versions of FB demos
hopefully final versions of FB demos
First working version of ssajoin for globals.

  - Need to run regression
Fixes in loop phis.
Merge branch 'master' into ssajoin
Fixes in SSA - using separate env for updated glob

  - Ambient vars are initialized.

  - Fixes in tests.
Adding some untracked tests.