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