Fix support for Watchify

Currently jadeify only registers the required jade file, not allowing watchify to rebuild or cache changes to the jade dependency tree.  This modification uses the Jade parser to create an array of the dependency tree of a required jade file and registers its dependencies as "files" for browserify and watchify.
Can we reuse the parser to compile from the parsed tree? Seems a shame that we compile (which presumably includes parsing) once, and then later parse again. /cc @ForbesLindesay.