Add javascript linter to build

[daveschaefer]

Rather than letting a bunch of potential errors come through, or having to go spot and fix all of the '==' uses by hand, let's hook up JSLint - https://github.com/douglascrockford/JSLint - to the build system and have it run on ever build.

[daveschaefer]

Note: this should happen after the 4.6.4 that fixes #59 . Unblocking signing and uploads is a much higher priority.