rebuild when a sub-bundle's file changes

workerify when paired with watchify does not
rebuild when the files in the workerify bundle
change.

This was due to two thingsi:

1) workerify was not emitting a 'file' event
   to notify watchify of the dependency

solved with: tmpvar/workerify/98503c2f73

2) watchify was not properly watching the
   dependencies of workerify

solved with this commit by unifying the strategy
for watching both the mfile and files emitted
by transforms.