commit: add --force-close-branch flag to close a non-head changeset
While closing branch from a changeset which is not a branch head
current implementation abort this action in every case but, there
can be the situations where the changeset is not a local head but
could be a remote head. This patch adds the functionality to bypass
the "abort: can only close branch heads" by introducing
Test case changes demonstrate the new functionality added.
Differential Revision: https://phab.mercurial-scm.org/D6490