Support for CoffeeScript source files in combination with coffeeify

When a .coffee source file is run through transforms [coffeeify, debowerify],
debowerify can operate upon it just as it would upon a .js source file with no
problems. This is stopped by the guard clause at the start of the module,
however, which only lets .js files through.

Completely removing that guard clause might be reasonable; as far as I know,
browserify only ever looks at  source files of some kind or another, and if
users have dropped in the appropriate transforms (coffeeify, liveify, and so
on) there's no reason not to run debowerify on those non-.js files as well.
I've made only the minimal change needed to get my CoffeeScript-based project
working right, though---dropping the line entirely is worth consideration
nonetheless.
Merge pull request #1 from 00Davo/coffee

Support for CoffeeScript source files in combination with coffeeify