tests: add test showing crash when shelving ghosted rename target
When you hg rename a file and then delete the rename target, `hg
shelve` will give you a traceback.
Note that the shelve succeeds and the shelve is correct, it's just the
update to the parent that fails (i.e. to the parent of the commit that
was created for the shelve).
This can be squashed into the next commit if the reviewer prefers.
Differential Revision: https://phab.mercurial-scm.org/D8045