Clarify that --out must come before any unknown command line flag

See issue #283 for background.

Review URL: https://github.com/google/traceur-compiler/issues/284

Closes #284.
getopt.js: simplify `nextchar` code.

Review URL: https://github.com/google/traceur-compiler/issues/292

Closes #292.
Remove Closure Library dependency

We no longer use Closure Library for testing.

Review URL: https://github.com/google/traceur-compiler/issues/285

Closes #285.