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

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

This commit was generated by cvs2svn to compensate for changes in r171169,
which included commits to RCS files with non-trunk default branches.

Import pf userland from OpenBSD 4.1 and (for ftp-proxy) libevent 1.3b as
a local lib.