Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

MFC: r256968, r256971, r256978

Improve SRV records support for the pkg(8) bootstrap:
- order srv records by priorities
- for all entries of the same priority, order randomly respect the weight
- select the port where to fetch from respect the port provided in the SRV
record

Allow to bootstrap by doing pkg add ./a/path/to/a/pkg_package.txz

Approved by: re (glebius)

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

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

Fix a bad calloc(3) call

MFC after: 2 weeks

Directly uses calloc(3) instread of malloc(3) + memset(3)

Reported by: Jeremy Chadwick <jdc@koitsu.org>
MFC after: 3 days

if PACKAGESITE url scheme is not 'file://', always try to revolv SRV records and
use them if any. It allows the bootstrap to use directly pkg.FreeBSD.org instead
of pkgbeta.FreeBSD.org

MFC after: 1 month