'Uses git commands to check if there is a newer version that the provided
commit hash. If there is a newer version it sets _num_commits_behind.'

def _check_for_new_version(self):

    (output, _, exit_status) = self._run_git(self._git_path, u'remote    update')
    if (not (exit_status == 0)):
        sickrage.srCore.srLogger.warning(u"Unable    to    contact    server,    can't    check    for    update")
        return
    (output, _, exit_status) = self._run_git(self._git_path, u'rev-parse    --verify    --quiet    "@{upstream}"')
    if ((exit_status == 0) and output):
        return output.strip()
