Dont log inotify missing error when using branch coloring

The error message about inotify being missing when branch coloring is
enabled was being logged for every directory and for every invocation
of powerline in a shell, without powerline-daemon. Dont log it, since
the log is printed to stderr when using powerline in a shell without
powerline-daemon. Also improve the error message on OS X. Fixes #578

powerline/lib/inotify.py

@@ -26,6 +26,8 @@ def load_inotify():
 			# if the one chosen by ctypes is compatible with the currently
 			# loaded one.
 			raise INotifyError('INotify not available on windows')
+		if sys.platform == 'darwin':
+			raise INotifyError('INotify not available on OS X')
 		import ctypes
 		if not hasattr(ctypes, 'c_ssize_t'):
 			raise INotifyError('You need python >= 2.7 to use inotify')

powerline/lib/tree_watcher.py

@@ -162,7 +162,7 @@ class TreeWatcher(object):
 		try:
 			w = INotifyTreeWatcher(path, ignore_event=ignore_event)
 		except (INotifyError, DirTooLarge) as e:
-			if logger is not None:
+			if logger is not None and not isinstance(e, INotifyError):
 				logger.warn('Failed to watch path: {0} with error: {1}'.format(path, e))
 			w = DummyTreeWatcher(path)
 		self.watches[path] = w