- 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

Fix -Wmissing-variable-declarations compiler warning.

Dont cast from char* to struct chrp_header* which has a bigger alignment
requirements. Copy it via union instead. Fixes a clang warning about
alignment.

Reviewed by: sobomax

The last big commit: let usr.sbin/ use WARNS=6 by default.

Revise markup.

Create section 8 man subdirectories for PowerPC.

Add device to access and modify Open Firmware NVRAM settings in
PowerPC-based Apple's machines and small utility to do it from
userland modelled after the similar utility in Darwin/OSX.

Only tested on 1.25GHz G4 Mac Mini.

MFC after: 1 month