fix watcher support: bundle.allFiles doesn't reset properly, eventually resulting in EMFILE errors on mac

The issue here is that the transform is called every time we run the bundle, but we only reset bundle.allFiles when we first create the bundle. Each time the file is changed and rebundled, the files get appended to bundle.allFiles, and the list explodes.
Merge pull request #5 from marcello3d/watcher

fix watcher support: bundle.allFiles doesn't reset properly, eventually resulting in EMFILE errors on mac

The issue here is that the transform is called every time we run the bundle, but we only reset bundle.allFiles when we first create the bundle. Each time the file is changed and rebundled, the files get appended to bundle.allFiles, and the list explodes.