Sourcemap option replumbing

Set options on mutable System object rather than arg to LoaderHooks.
Avoid exception on anonymous modules requesting source maps in repl.
Pass source-map via destructing rather than on options (partial).

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/741

Closes #741.
Fix SyntaxErrorReporter and add unit test

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/745

Closes #745.