Fix repl options menu

Fixes #1334
Block binding: Handle nested scopes better

Issue #1358
0.0.66
Pass metadata to REPL onFailure.

Show transcoding if the error is an evaluation error.

Fixes #1373

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1375

Closes #1375, closes #1373.
Use Compiler API in Loader.

Now our command line always runs through our Compiler API.

Fixes #1324

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1355

Closes #1355, closes #1324.
Make sure native symbols work

Do not overwrite the native Symbol if present.

Instead of enforcing that our shim symbols are non enumerable we
now generate code to filter out symbols for for-in loops. This allows
us to remove $traceurRuntime.setProperty since it is now OK to use
the standard browser [[Set]].

For the class runtime we need to iterate over the symbols too.

Fixes #1330
Code review cleanup