resolve: add option to warn/abort on -m with unresolved conflict markers When a user is dropped out of Mercurial to a terminal to resolve files, we emit messages like: conflicts while merging file1! (edit, then use 'hg resolve --mark') conflicts while merging file2! (edit, then use 'hg resolve --mark') We don't mention a file name in the hint, so some users might do something like `$EDITOR file1; hg resolve --mark`, see that it says "(no more unresolved files)" and forget to deal with file2 before running the next command. Even if we did mention a file name in the hint, it's too easy to forget it (maybe the merge spans a couple days or something). This option lets us inform the user that they might have missed something. In the scenario above, the output would be something like: warning: the following files still have conflict markers: file2 (no more unresolved files) Differential Revision: https://phab.mercurial-scm.org/D4035