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.
Here is how export and mq write the "Parent" header:
mq: # Parent XXXXX
export: # Parent XXXXX
then import expects exactly 2 spaces while mq tolerates one or more. So "hg
import --exact" truncates mq generated patches header by one character and
fails. This patch aligns import "Parent" header parsing on mq one. I do not
expect spaces in parent references anytime soon.
Reported by Stefan Ring <stefanrin@gmail.com>
