maint.mk: ignore multi-line copyright in NEWS
The old algorithm did not work for projects like m4 that used
long-hand copyright years that wrapped lines. Meanwhile, this
change has no impact to single-line copyrights, like coreutils.
Changing the rest of the footer, such as bumping from GFDL 1.2
to GFDL 1.3, will still require the developer to rerun
'make update-NEWS-hash' to get the hash back in sync, but that
is probably less frequent.
* top/maint.mk (NEWS_hash): Add immunity to multi-line copyright.
Signed-off-by: Eric Blake <ebb9@byu.net>
(cherry picked from commit
c4b45631bce0034e4433a9f421cf16fe803c51f3)