Log Message:
gajim: Add missing dependency to certifi and do not override __version__

- certifi module is needed despite not explicitly specified as a
  dependency in setup.py (probably a line about it should be added
  in setup.py too and shared with upstream).
- Do not override __version__ if git is found. This leads to possible PLIST
  problems due non-matching EGG_INFODIR.

Problem and patch by Jonathan Schleifer via PR pkg/53731 (PLIST problem a bit
reworked by leot).