keyword: (bugfix) only set changenode for kwtemplater when committing kwexpand must always obtain changenode from filectx, otherwise current changenode is expanded in every file. Also fixes "hg cat <more than 1 file>".

test-mq-header: don't fail with different patch(1) At least under FreeBSD patch(1) won't fail on empty patch and will print 'Hmm...' warning instead. Sanitize output so tests won't fail unexpectedly.