Merge branch 'js/complete-checkout-t'

The completion script (in contrib/) has been taught to treat the
"-t" option to "git checkout" and "git switch" just like the
"--track" option, to complete remote-tracking branches.

* js/complete-checkout-t:
  completion(switch/checkout): treat --track and -t the same

diff --cc contrib/completion/git-completion.bash
Simple merge

diff --cc t/t9902-completion.sh
Simple merge