Update stable/9 to -RC1 in preparation of branching releng/9.3

Approved by:	re (implicit)
Sponsored by:	The FreeBSD Foundation
Update __FreeBSD_version now that releng/9.3 is branched.

Approved by:	re (implicit)
Sponsored by:	The FreeBSD Foundation
Switch stable/9 back to -PRERELEASE now that releng/9.3 is branched.

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