- 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

MFC r279326:
Use pthread_mutex_trylock(3) to implement mtx_trylock(3).

MFC r279318:
Check that the pointer to the thread return value is not NULL before
dereferencing. NULL is allowed by C11 and must be handled.

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

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

Pull up vendor changes to mdoc(7)

This switches us to using -isoC-2011 as the symbol name which is used by
groff and mdocml. It follows the change to 4 digit years as done with
IEEE Std 1003 post-1999.

MFC after: 2 weeks (groff changes only)

Add libstdthreads.

This library implements the C11 threads interface on top of the pthreads
library. As discussed on the lists, the preferred way to implement
this, is as a separate library.

It is unlikely that these functions will be used a lot in the future. It
would have been easier if the C11 working group standardized (a subset
of) pthreads and clock_nanosleep(). Having it as a separate library
allows the embedded people to omit it from their system.

Discussed on: arch@, threads@