Fixed writing XML with non-ASCII characters

Error was:

  File ".../0repo/repo/incoming.py", line 189, in process
    stream.write(new_xml)
UnicodeEncodeError: 'ascii' codec can't encode character u'\xe4' in position
528: ordinal not in range(128)

Reported by Bastian Eicher.
Fixed handling of non-ASCII characters in commit messages on Windows

See http://bugs.python.org/issue1759845