- 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

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

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

Add some regression tests for printf() with positional arguments.
The first test comes from OpenBSD, and the others are additions or
adaptations.

This is based on OpenBSD's
src/regress/lib/libc/sprintf/sprintf_test.c, v1.3.
I deliberately did not use v1.4 because it's bogus.