tests: show that interactive shelve can leave the repo with a merge state

If part of a file is shelved (as we already do in a test), there will
be an unfinished merge state left after `hg shelve` finishes. There
should never be a merge conflict and there should never be a reason
that the user would like to re-resolve conflicts, so we should clear
that state (see next patch).

Differential Revision: https://phab.mercurial-scm.org/D9334

tests/test-shelve.t

@@ -810,6 +810,9 b' Test interactive shelve'
   ? foo/foo
   $ hg bookmark
    \* test                      (4|13):33f7f61e6c5e (re)
+BROKEN: there shouldn't be a merge state
+  $ hg resolve -l
+  R a/a
   $ hg unshelve
   unshelving change 'test'
   temporarily committing pending changes (restore with 'hg unshelve --abort')