System.set and System.getForTesting.

System.set() takes a module.
System.getForTesting() is a backdoor, needed for test/unit once
    we merge static and dynamic modules.
Drive-by: fix Makefile for runtime-related rules.

Review URL: https://github.com/google/traceur-compiler/pull/658

Closes #658.
Report compile errors without throw, fixes #662

Review URL: https://github.com/google/traceur-compiler/pull/663

Closes #663.
Attach comments during parse