Use relative import for own inotify module.
Drop own implementation of inotify, keeping only a compatibility wrapper.

Maintaining our own implementation of inotify is not a good idea,
better reuse an existing implementation. As we are using twisted.internet
anyway, we use twisted.internet.inotify, which is quite similar to our
implementation.

This includes the following incompatible change:
* coherence.external.inotify.Watch is gone

The one test for Watch has been removed, one has been adopted, all tests
pass.
Enhance backward-compatibility for INotify.watch().
Fix error/typo in INotify.watch()
Make mini-test in body of extern.inotify work.
Watch /tmp/aaa in mini-test in body of extern.inotify instead of /tmp.

Watching /tmp may be to much and contain e.g. sockets.
Update copyright and docu.
Add deprecation warning.
Drop most of the compatibility wrapper for inotify.

Sorry, but the old coherence.external.inotify implementation had some
nasty bugs. So it's better to make a rather hard cut instead of
trying to keep the bugs.
Clean up code of test-case.
Adopt fs_storage to the changed inotify interface.

This still needs to be tested.
Finished feature remove-own-inotify.
Fix directory exists error.