status: advertise --abort instead of 'update -C .' to abort a merge
status has a part where it shows the conflict information and how to continue or
abort. Couple of release ago, we got merge --abort and we should advertise that
instead of 'hg update -C .' which is kind of ugly.
I know we need to unify the logic here.
Differential Revision: https://phab.mercurial-scm.org/D4168