Fix retrieval of pictures on Python 2.x
Document the value for the group_getGroups argument

The only usage of this function I could find was added in commit 8812cc1
of wazzap, but that commit has never been merged. Add the only useful
information of that commit to Yowsup itself, for future reference.
Print "connecting to" message using the debugger

This allows clients to disable this message
Merge pull request #152 from oxan/misc-fixes

Miscellaneous fixes