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

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

Renumber clauses to reduce diffs to other versions

NetBSD, OpenBSD, and Android's Bionic number the clauses 1 through 3,
so follow suit to make comparison easier.

Remove license clause 3 to agree with the now-standard BSD license.

Prompted by: Glenn Halperin, Symbian Software

MFp4: Make `spanp' const.

Add an implementation of wcstok(), based on strtok_r().