Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

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)

Revamp libpthread so that it has a chance of working in an SMP
environment. This includes support for multiple KSEs and KSEGs.

The ability to create more than 1 KSE via pthread_setconcurrency()
is in the works as well as support for PTHREAD_SCOPE_SYSTEM threads.
Those should come shortly.

There are still some known issues which davidxu and I are working
on, but it'll make it easier for us by committing what we have.

This library now passes all of the ACE tests that libc_r passes
with the exception of one. It also seems to work OK with KDE
including konqueror, kwrite, etc. I haven't been able to get
mozilla to run due to lack of java plugin, so I'd be interested
to see how it works with that.

Reviewed by: davidxu

Use GCC's __attribute__ ((constructor)) mechanism to invoke the pthread
startup code rather than a static C++ object since c++ seems to be broken.

This doesn't seem to work for staticically linked program just yet, I'll
give that some more work when I get a chance.