- Copy stable/10@285827 to releng/10.2 in preparation for 10.2-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.2.
- Update default pkg(8) configuration to use the quarterly branch.[1]

Discussed with: re, portmgr [1]
Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

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

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

Add initial Atheros AR91XX support.

This works well enough to bring a system up to single-user mode
using an MDROOT.

Known Issues:

* The EHCI USB doesn't currently work and will panic the kernel during
attach.
* The onboard ethernet won't work until the PLL routines have been
fleshed out and shoe-horned into if_arge.
* The WMAC device glue (and quite likely the if_ath support)
hasn't yet been implemented.