Copy stable/11@r303970 to releng/11.0 as part of the 11.0-RELEASE
cycle.

Prune svn:mergeinfo from the new branch, and rename it to RC1.

Update __FreeBSD_version.

Use the quarterly branch for the default FreeBSD.conf pkg(8) repo and
the dvd1.iso packages population.

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

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Let l64a() properly null terminate its result.

Though the buffer used by l64a() is initialized with null bytes,
repetetive calls may end up having trailing garbage of previous
invocations because we don't end up terminating the string.

Instead of importing NetBSD's fix, use this opportunity to simplify this
function dramatically, for example by just storing the Base64 character
set in a string. There is also no need to do the bitmasking, as we can
just use the proper integer type from <stdint.h>.

MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D6511

Add a64l(), l64a(), and l64a_r() XSI extentions. These functions convert
between a 32-bit integer and a radix-64 ASCII string. The l64a_r() function
is a NetBSD addition.

PR: 51209 (based on submission, but very different)
Reviewed by: bde, ru