Release notes for 9.4.3, 9.3.8, 9.2.12, 9.1.17, 9.0.21.

Release notes for 9.4.3, 9.3.8, 9.2.12, 9.1.17, 9.0.21.

Also sneak entries for commits 97ff2a564 et al into the sections for
the previous releases in the relevant branches.  Those fixes did go out
in the previous releases, but missed getting documented.