server terminates if user cannot chown

[dansan]

When zrsyncd is run as non-root user, and the UID of a source file/dir differs, it tries a chmod, fails, displays a traceback and quits:

2016-08-19 01:30:52 zrsyncd.cmp_node:504  DEBUG [24971] does not exist: u'/tmp/mytarget'
2016-08-19 01:30:52 zrsyncd.mkdir:627  DEBUG [24971] mkdir(u'/tmp/mytarget'); chown(); utime()
2016-08-19 01:30:52 zrsyncd.chown:623  DEBUG [24971] chown(u'/tmp/mytarget', 2311, 5001)
Process sync_server:
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/usr/lib/python2.7/multiprocessing/process.py", line 114, in run
    self._target(*self._args, **self._kwargs)
  File "/home/daniel/.zrsync/zrsync/zrsync/zrsyncd.py", line 699, in run
    reply["tree_diff"] = self.sync_tree(src_tree, request["no_delete"])
  File "/home/daniel/.zrsync/zrsync/zrsync/zrsyncd.py", line 475, in sync_tree
    res = self.cmp_node(node)
  File "/home/daniel/.zrsync/zrsync/zrsync/zrsyncd.py", line 513, in cmp_node
    node["st_atime"], node["st_mtime"])
  File "/home/daniel/.zrsync/zrsync/zrsync/zrsyncd.py", line 629, in mkdir
    self.chown(dirname, uid, gid)
  File "/home/daniel/.zrsync/zrsync/zrsync/zrsyncd.py", line 624, in chown
    os.lchown(name, uid, gid)
OSError: [Errno 1] Operation not permitted: '/tmp/mytarget'

zrsyncd should instead send a note back to the client, which should display a warning.