minirst: handle edge in hunting for parents
test for "hg help -c config" in help config
``section``
-----------
section text
``def1``
definition of def1
$ hg help scope.def1
should list this paragraph, but not section text below...
section text
``def2``
definition of def2
$ hg help scope.def2
should list this paragraph, but not section text below...
section text
$ hg help scope.section should show everything from the first
section text to this last line.
``section2``
------------