Refactored recursiveModuleCompile with promises.

Did some simplification of existing logic in recursiveModuleCompile, to
use promises more canonically.
Fix the logic in recursiveModuleCompileToSingleFile to always revert the
cwd no matter what.
fix a typo in SuperTransformer
Use ParseTree.isDirectivePrologue() to simplify PrependStatement
Add support for member variable initializers