Fix a couple of bugs in the inotify file watcher's skip_files logic.

Summary:
Testign the inotify file watcher using a Vagrant box uncovered a couple of bugs
that were preventing it from ever triggering a reload of the module. This
change fixes them.

I also added some extra logging statements that will get emitted when the file
watchers finish initializing because I discovered that the inotify file watcher
takes a really long time to start up. I'm hoping the abysmal startup times I
observed (minutes!) were localized to my Vagrant box, although I gave it 2 GB
of RAM and had nothing else major running on my machine. If it's this bad for
"real" Linux users I might need to look at further optimizing it.

Test Plan:
1. Set up a Linux environment for webapp using Vagrant
2. Added extra logging statements so I could tell which paths were getting skipped at initialization time and file-change time
3. Ran `make serve` and waited for the "Started InotifyFileWatcher" message
4. Performed the usual file watcher tests, confirmed that it now has the same reloading behavior as the fsevents and mtime file watchers

Reviewers: benkraft

Reviewed By: benkraft

Differential Revision: http://phabricator.khanacademy.org/D9858