- 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: r263648, r264789, r266636

This brings:
- schema validation
- xpath-like interface for ucl objects

Adapt pkg(7) to the new libucl API