* 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

winsup/cygwin/cygthread.h

@@ -8,7 +8,7 @@ details. */
 
 class cygthread
 {
-  DWORD avail;
+  LONG avail;	/* 1: available, 0: ininitialized, -1: not available */
   DWORD id;
   HANDLE h;
   HANDLE ev;