Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Repo copy libpthreads to libkse.
This introduces the WITHOUT_LIBKSE nob,
and changes WITHOUT_LIBPTHREADS to mean with neither threading libs.
Approved by: re(kensmith)

Eliminate two pushl by using call instruction directly, this really
helps branch predict a lot for INTEL P4.

Approved by: re (scottl)

Take the same approach for i386 as that for ia64 and amd64. Use
the userland version of [gs]etcontext to switch between a thread
and the UTS scheduler (and back again). This also fixes a bug
in i386 _thr_setcontext() which wasn't properly restoring the
context.

Reviewed by: davidxu

Add architecture dependent atomic ops (atomic_swap only), KSE specific
data, and userland versions of [gs]etcontext().

Modify the UTS entry and exit functions to account of FPU validity
and format.

In _thread_enter_uts, fix eflags saving bug.
In _thread_switch, set current thread pointer in kse mailbox
only after all registers copied out of thread mailbox, kernel will do
upcall at trap time, if set current thread pointer before loading all
registers from thread mailbox, at trap time, the thread mailbox data
will be overwritten by kernel, result is junk data is loaded into CPU.

Adjust code for new mailbox format.

Reviewed by: deischen, mini

Use KSE to schedule threads.