- Copy stable/10@296371 to releng/10.3 in preparation for 10.3-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.3.
- Update default pkg(8) configuration to use the quarterly branch.

Approved by: re (implicit)

MFC r274073:
Follow-up to r255036; remove beforeinstall directives from bsdconfig(8)
Makefile's, fixing concurrent installworld (`make -j17 installworld').

Reviewed by: delphij
Thanks to: delphij, emaste

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Add the beginnings of the old networking services functionality of
sysinstall(8). The UI for this will come later while this exposes the
functionality to the scripted interface. Tested successfully to first
install the pcnfsd package from the `Latest' repository, and second to
configure mountd_flags="-n" in rc.conf(5).

Move major includes into /usr/share/bsdconfig for easy external access.

Reviewed by: adrian (co-mentor)
Approved by: adrian (co-mentor)