Update URL for Closure compiler.
Don't do dead code removal in Data.JSTarget.Optimize.

GHC does a decent enough job of this, and it turns out some of the code we
removed wasn't quite dead yet.
Don't use _ as a generic State# var anymore.

It could conceivably mess up dependencies the optimizer needs to avoid doing
stupid things.
Add haste-inst build flag when building stuff with haste-inst.
Add back stub version of System.Posix.Internals.
Add stubs for FD <-> Handle conversions. Fixes #63.
Rename realWorld dummy var to _.
Add back generic "_" dummy var - it's needed in some places.