maint: summarize highlights of 1.4.18 release

* NEWS: Add some blurbs.
* .prev-version: Record previous version.
* cfg.mk (old_NEWS_hash): Update.

Signed-off-by: Eric Blake <eblake@redhat.com>
[this is a mish-mash of two patches from branch-1.4:]
(cherry picked from commit 658427104bbe515249f728d8524e975167e6533d)
(cherry picked from commit e0140bd91ce0d2dfcdd1df22472d81ed13489d46)
3 files changed