sequencer: teach autostash apply to take optional conflict marker labels
Add label_ours, label_theirs, label_base, and stash_msg parameters to
apply_autostash_ref() and the autostash apply machinery so callers can
pass custom conflict marker labels through to
"git stash apply --label-ours/--label-theirs/--label-base", as well as
a custom stash message for "git stash store -m".
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>