93eca2533d2a and 1deb493773a1 fixed issue4453 with a simple insertplainheader
function that fixed the regression but didn't make the implementation more
stable.
Now we introduce plain header handling similar to how we handle hg patches. The
whole header is scanned for fields to update while determining the best
position for inserting the field if it is missing. It also makes sure there is
an empty line between headers and body.
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.
The tests in test-annotate.t and test-import-git.t that relied on trailing
space in a file created by a here string is now masked by a literal 'EOL'
string that is removed.
