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.
Globbing is usually used for filenames, so on windows it is reasonable and very
convenient that glob patterns accepts '\' or '/' when the pattern specifies
'/'.
The test sometimes failed because f4.bat wasn't dirty. I'm not sure whether it
should or shouldn't be dirty, but the extension is broken and deprecated and we
just want to see the deprecation warning, so now we just avoid showing the
dirtyness.
