- 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

Extend the unix gc regression test to cover the case of r216150.

Requested and reviewed by: rwatson
MFC after: 1 week

In UNIX domain socket GC regression test, after setting a socket
non-blocking, EINPROGRESS is an acceptable result from connect().

Add regression tests for UNIX domain socket garbage collection. Should be
run from single-user mode, as they look at global open file and inflight
descriptor counts to check for leaks.