Partial fix to issue #142

Introduces a new, different error:

    Traceback (most recent call last):
      File "test.py", line 188, in test_simple_conflict
        commit2 = bizarro.repo.save_working_file(*args2)
      File "/Users/migurski/Sites/tmp/CMS/bizarro/repo.py", line 77, in save_working_file
        clone.remotes.origin.push(clone.active_branch.name)
      File "/Users/migurski/Sites/tmp/CMS/venv-cms/lib/python2.7/site-packages/git/repo/base.py", line 551, in active_branch
        return self.head.reference
      File "/Users/migurski/Sites/tmp/CMS/venv-cms/lib/python2.7/site-packages/git/refs/symbolic.py", line 244, in _get_reference
        raise TypeError("%s is a detached symbolic reference as it points to %r" % (self, sha))
    TypeError: HEAD is a detached symbolic reference as it points to '320ac0ab2ed85f0e65ad734e2a72863a526db5be'