- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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 some more diagnostic codes.

Obtained from: Qualcomm Atheros

Reserve a new diagnostic code for the channel survey code I'll add soon.

Break out the diagnostic codes from ah_internal.h and place them in ah_diagcodes.h.

Since we now have the source code, there's no reason to hide the diag codes
from other areas.

They live in the HAL as they form part of the HAL API and should still be treate
as "potentially flexible; don't publish as a public API." But since they're
already used as a public API (see follow-up commit), we may as well use
them in place of magic constants.