- 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)

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

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

Add bsd.port.options.mk, a stub to include parts of bsd.port.mk that handle
OPTIONS resolving. This will allow us to load bsd.port.mk in port Makefiles in
three steps (options, pre, post), allowing us to manipulate USE_* flags
conditionally on OPTIONS values.

With hat: portmgr
Reviewed by: ru
MFC after: 1 week