Copy stable/11@r349022 to releng/11.3 as part of the 11.3-RELEASE
cycle.
Update releng/11.3 from BETA3 to RC1.
Switch the default dvd1.iso pkg(8) repository from latest to
quarterly.
Bump __FreeBSD_version.
Prune vestigial svn:mergeinfo from the new branch.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation