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

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

Update subversion-1.8.0 -> 1.8.1. Update supporting
components: apr-1.4.6 -> 1.4.8 and apr-util-1.4.1 -> 1.5.2.

This is a post point-zero bug-fix / fix-sharp-edges release, including
some workarounds for UTF-8 for people who haven't yet turned on WITH_ICONV.

Import Apache apr-util-1.5.2 into vendor staging area.