Forward-port 0.2.4.22 changelog
Document that we're incrementing version numbers in maint.

(ticket 9553)
Bump maint-0.2.4 version to 0.2.4.22-dev

(See discussion on #9553)
Merge remote-tracking branch 'origin/maint-0.2.4'

This is an "ours" merge, to avoid taking the commit that bumped
maint-0.2.4's version to 0.2.4.22-dev.