- 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

Add a second pass to the close-before-accept test using a call to the
tcp drop sysctl. This should exercise the ECONNABORTED accept case.

Add a regression test to exercise the case where accept() is called and
the next waiting socket has had a close on the remote endpoint already.