Interpreter: handle --help and -h correctly.

This was previously considered an error by the argv filter, as
commander.js implements the flags, but doesn't return anything for them
in optionFor.

Review URL: https://github.com/google/traceur-compiler/issues/303

Closes #303.
Add missing `to` in `path.relative(from, to)` in `compileToDirectory`.

Commit joyent/node@089ec5861357 to node broke this non-standard shortcut.

Fixes #304

Review URL: https://github.com/google/traceur-compiler/issues/306

Closes #306, closes #304.
Make sure `getopt` errors on invalid long options.

Before, `getopt` was returning invalid long options as arguments.

Examples:

```sh
./traceur --not-a-filename.js --"has spaces" --= --? --^ --...
```

Review URL: https://github.com/google/traceur-compiler/issues/291

Closes #291.
Add missing `node_modules` dependency to `Makefile`.

`$(TPL_GENSRC_DEPS)` depends on `node_modules`. This was causing `make`
to fail with a fresh repo clone. This isn't the cleanest solution, but
there may not be one, since there is a catch-22 here. We can't know the
full set of prerequisites without at least initializing the
`node_modules` prerequisite.

Discussion link:
https://groups.google.com/d/msg/traceur-compiler-discuss/zWvNP_6gHKg/FlcmRC2MwmsJ

Review URL: https://github.com/google/traceur-compiler/issues/308

Closes #308.