- 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

Rework the handling of the children for the pthread_vfork_test. The
trivial handler for SIGCHLD is installed, and SIGCHLD is blocked, to
not abandon our zombies to init(8). This way, the zombies are around
slightly longer, allowing to actually exercise the logic for p_pwait
use by the test.

MFC after: 1 week

This is simple testing program for revision 185647.
It invokes multiple parallel threads and each thread calls vfork()
system call.

Approved by: kib