Atomic replace fails on mounted file system

[Sander Maijers]

Saving a page of a Zim (0.61) notebook to an SSHFS FUSE mount on Linux of a Windows SSH (SFTP) server fails in the method zim.fs.UnixFile#_on_write as an OSError is raised from:
  os.rename(tmp, self.encodedpath)

The comment:
# On Unix, for rename() if dest already exists it is replaced in an
# atomic operation. And other processes reading our file will not
# block moving it :)
seems not to hold true in this case.

A straightforward patch is to replace said line with:
  try:
   os.rename(tmp, self.encodedpath)
  except OSError:
   if os.path.exists(self.encodedpath):
    os.unlink(self.encodedpath)
    os.rename(tmp, self.encodedpath)

This is not a particularly robust solution because the exception raised is rather broad (OSError) and because further exceptions raised are not handled in this code. Finer-grained IO exception classes and a cross-platform atomic file moving function os.replace() are only available in Python 3.3+. See: http://bugs.python.org/issue8828

[Jaap Karssenberg (jaap.karssenberg)]

Probably should add a (hidden) config option to disable replace on such file systems.