347 Test with :mergediff conflict markers

   348   $ hg resolve --unmark

   349   $ hg resolve --re-merge -t :mergediff file2

   350   merging file2

   351   warning: conflicts while merging file2! (edit, then use 'hg resolve --mark')

   352   [1]

   353   $ hg resolve -l

   354   U file1

   355   U file2

   356   $ hg --config commands.resolve.mark-check=abort resolve -m

   357   warning: the following files still have conflict markers:

   358     file2

   359   abort: conflict markers detected

   360   (use --all to mark anyway)

   361   [20]

   362   $ hg resolve -l

   363   U file1

   364   U file2