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

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

Per Regents of the University of Calfornia letter, remove advertising
clause.

# If I've done so improperly on a file, please let me know.

Emulate ldq and stq (load/store long double) instructions. GCC has started
using these to load long doubles, but they aren't implemented in hardware
on (at least) UltraSPARC I and II machines.
Emulate popc in the user trap handler as well.
Re-arrange slightly to make support functions more accessible.

Reviewed by: tmm

Fix the style of the SCM ID's.
I believe have made all of libc .c's as consistent as possible.

Remove 'register' keyword.

Add userland floating point emulator code for sparc64. This is a port
of the (never committed) in-kernel version (with some optimizations and
cleanups), which in turn was ported from NetBSD.