Crash when watched file is missing

[lieryan]

Some text editors delete or moves a file before saving the edited file. autonose occasionally crash when it tries to detect modification time while the file is temporarily deleted.

Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/threading.py", line 763, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/path/to/autonose/shared/state.py", line 158, in process_events_forever
    self._process_changes(new_events)
  File "/path/to/autonose/shared/state.py", line 168, in _process_changes
    map(self._process_change, changes)
  File "/path/to/autonose/shared/state.py", line 201, in _process_change
    map(self._inspect, existing)
  File "/path/to/autonose/shared/state.py", line 268, in _inspect
    self._check_for_change(rel_path)
  File "/path/to/autonose/shared/state.py", line 279, in _check_for_change
    if file_state.stale():
  File "/path/to/autonose/shared/file_state.py", line 24, in stale
    return self._get_modtime() != self.modtime
  File "/path/to/autonose/shared/file_state.py", line 21, in _get_modtime
    return os.stat(file_util.absolute(self.path)).st_mtime
OSError: [Errno 2] No such file or directory: '/path/to/project/tests.py'