- Copy stable/10@296371 to releng/10.3 in preparation for 10.3-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.3.
- Update default pkg(8) configuration to use the quarterly branch.

Approved by: re (implicit)

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

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

Revert revision 214007, I realized that MySQL wants to resolve
a silly rwlock deadlock problem, the deadlock is caused by writer
waiters, if a thread has already locked a reader lock, and wants to
acquire another reader lock, it will be blocked by writer waiters,
but we had already fixed it years ago.

Set default type to PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP, this
is the type we are using.

s/||/&&

Add pthread_rwlockattr_setkind_np and pthread_rwlockattr_getkind_np, the
functions set or get pthread_rwlock type, current supported types are:
PTHREAD_RWLOCK_PREFER_READER_NP,
PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP,
PTHREAD_RWLOCK_PREFER_WRITER_NP,
default is PTHREAD_RWLOCK_PREFER_WRITER_NONCECURSIVE_NP, this maintains
binary compatible with old code.

WARNS level 4 cleanup.

- Add libthr but don't hook it up to the regular build yet. This is an
adaptation of libc_r for the thr system call interface. This is beta
quality code.