With this change resolve and revert produce consistent output when run with no
arguments:
$ hg resolve
abort: no files or directories specified
(use --all to remerge all files)
$ hg revert
abort: no files or directories specified
(use --all to revert all files)
Many tests didn't change back from subdirectories at the end of the tests ...
and they don't have to. The missing 'cd ..' could always be added when another
test case is added to the test file.
This change do that tests (99.5%) consistently end up in $TESTDIR where they
started, thus making it simpler to extend them or move them around.
Without specifying the parent revision of the working copy, users will
update to tip, which is most likely the other head they were trying to
merge, not the revision they were at before the merge.
