Fix `make syntax-check'.

Fix `make syntax-check'.

There are two errors caught by make syntax-check currently.

First, the recent make update-copyright
(d78a7dd95fed24e417dfb4d08124a9ce7c1f7d1e) missed autoconf.texi, I
think because there are a bunch of .texi files in doc/ whose copyright
years should *not* be updated (e.g. standards.texi, fdl.texi) and the
exclusion pattern is too broad.  I can't actually *find* the exclusion
pattern in the twisty maze of .mk files, all alike, so I just manually
updated autoconf.texi.

Second, it objects to an edit to an old section of NEWS.  This is
because of d3dcd5895d64f6c86275c9333e2760a867e540e7, which is a
legitimate change (replacing http:// with https:// in a URL) so the
correct action is to change old_NEWS_hash to match.

	* doc/autoconf.texi: Update copyright year.
	* cfg.mk (old_NEWS_hash): Update to acknowledge commit
	d3dcd5895d64f6c86275c9333e2760a867e540e7.