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

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

Use __FBSDID().

Further GC of M_STRING, missed previously.

Replace license with two-clause BSD; an old license template with three
clauses was used by mistake.

Pass a malloc type into the libkern strdup() implementation explicitly,
so that callers can specify what malloc pool the resulting memory
should come from.

Requested by: phk

Add an implementation of strdup() to libkern. Allocated memory is of
type M_STRING, now defined in malloc.h. Useful when string parsing
must occur using the kernel strsep() and we want to avoid toasting
the source string.

Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories