commands: only warn when reopening the workdir's branch
When commiting, a check is made to see if one of the parents is a
closed head. However this did not check that the branch of the commit
is the same as the closed head, so one could get a warning message on
the sequence
hg commit --close-branch
hg branch new-branch
hg commit
or when merging in a closed head.
Section.KeY=Case Sensitive
Section.key=lower case