Rebased till PG commit 7ac0069

Last-minute updates for release notes.

Add entries for v11 changes that went in post-stamping, but before
the final wrap.

Stamp 10.6.

Stamp 9.6.11.

Stamp 9.5.15.

Stamp 9.4.20.

Stamp 9.3.25.

rebase 30 oct 2018

Stamp 11.0.

Stamp 11rc1.