Fix traceback on .../msgN/ url... ...this requests the file content and for apache mod_wsgi produced a traceback because the mime type is None for messages, fixes issue2550586, thanks to ThomasAH for reporting and to Intevation for funding the fix.

#!/usr/bin/env python
import zlib, base64, sys
print base64.encodestring(zlib.compress(sys.stdin.read()))