obsolete: refuse to push divergent changeset
As other troubles `unstable` and `bumped`. Followup patches may simplify the
push code with unification of "obsolescence troubles" handling.
hide outer repo
$ hg init
$ echo '[Section]' >> $HGRCPATH
$ echo 'KeY = Case Sensitive' >> $HGRCPATH
$ echo 'key = lower case' >> $HGRCPATH
$ hg showconfig Section
Section.KeY=Case Sensitive
Section.key=lower case