Fixed memory leak from '--watch' flag.

As I initially feared, we were actually nesting closure environments with each new `getSourceFile`.

Fixes #366.
Addressed code review feedback.
Style and comments.
Merge pull request #367 from Microsoft/theDisintegrationOfThePersistenceOfMemory

Fixed memory leak when using '--watch' flag.
fixed build breaks in perftc
Merge branch 'master' into bom