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.
This removes use of unknown files for building the synthetic working
directory manifest used by manifestmerge. Instead, we adopt the
strategy used by _checkunknown.
Side-effect: unknown files are no longer moved by remote directory
renames, and now are left alone like ignored files.
Globbing is usually used for filenames, so on windows it is reasonable and very
convenient that glob patterns accepts '\' or '/' when the pattern specifies
'/'.
