Make sure all release note files have a single trailing empty line

Make sure all release note files have a single trailing empty line

This is needed so we can assemble a complete release notes file via a
command like:

cat $(/bin/ls -1 doc/RelNotes/v*.txt | tac) | gzip -9n > NEWS.gz

Signed-off-by: Theodore Ts'o <tytso@mit.edu>