* cygthread.h (cygthread::avail): Make LONG for easier use with Interlocked*

* cygthread.h (cygthread::avail): Make LONG for easier use with Interlocked*
functions.
* cygthread.cc (cygthread::init): Eliminate unneeded muto.
(cygthread::operator new): Don't lock.  Instead change use of avail variable
into tri-state: available (1), not available (-1), uninitialized (0).
(cygthread::terminate_thread): Set avail to uninitialized.
(cygthread::detach): Eliminate local 'avail'.  Always set avail to 1 unless
signalled.
* cygthread.cc (cygthread::operator new): Be more defensive when messing with