[1.6.x] Bump version for 1.6.4 bugfix release.
[1.6.x] Post release version bump.
[1.6.x] Added dates to release notes of today's release.

Backport of 68d264059a from master
[1.6.x] Added stub release notes for 1.6.5.

Backport of 650065f0ef from master