"git status" can spend a lot of cycles to compute the relation
between the current branch and its upstream, which can now be
disabled with "--no-ahead-behind" option.
* jh/status-no-ahead-behind:
status: support --no-ahead-behind in long format
status: update short status to respect --no-ahead-behind
status: add --[no-]ahead-behind to status and commit for V2 format.
stat_tracking_info: return +1 when branches not equal