Fix: Fixes no-unused-vars to check /*globals*/ (Fixes #955)

Fixes #955.

This changes the default back to the correct `"all"` for the **no-unused-vars** rule; it had been set to `"locals"` at some point.

It also augments the rule (which according to @nzakas should have been there all along, thus this is a Fix) to check for unused explicitly declared globals via `--global` or `/* global */`. This probably never worked before, since the plumbing wasn't really in place.
These three tests improperly assumed that the environmental configs wouldn't affect their tests and fail with the new global check; --reseting sandboxes them without affecting their outcomes.