Added base/file_lock.h
Added base/fs_notifier, a wrapper around inotify.
Started earsing previous events from the fs_notifier cache.
Reading new events over top of the old ones left in the buffer
can lead to the new events looking a little misleading. Erasing
before reading seems safer.
base/fs_notifier.test: Use modern construct for making unique pointers
Merge pull request #246 from cmaloney/inotify

RAII wrapper around Linux inotify