Fix inconsistent handling of plain header separation in mq patcheader - and
contrary to 05acc6157816, do it in the direction of having an empty line
between header and description. Plain patches are like mails and should thus
have an empty line between headers and body in compliance with RFC 822 3.1.
There would in some cases be an empty line between headers and the description -
that does not seem right.
There should also be an empty line between description and diff - but that was
missing.
These two mistakes would sometimes make it up for each other so we fix both at
once to just show the improvement.
Instead of writing an extra newline when writing a header line, write an extra
line when it not is written as a part of the description but is necessary
anyway.
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.
