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

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

Correct decoding a string containing '/'.

PR: 97485
Submitted by: Mikko Tyolajarvi < mbsd at pacbell dot net >

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