* fhandler.h (class fhandler_pty_master): Add master_thread member.

* fhandler_tty.cc (fhandler_pty_master::close): Properly detach from
	master thread.
	(fhandler_pty_master::setup): Store cygthread pointer of pty master
	control thread in master_thread.  Don't zap thread handle.

winsup/cygwin/fhandler.h

@@ -1125,6 +1125,7 @@ class fhandler_pty_master: public fhandler_tty_common
 {
   int pktmode;			// non-zero if pty in a packet mode.
   HANDLE master_ctl;		// Control socket for handle duplication
+  cygthread *master_thread;	// Master control thread
 
 public:
   int need_nl;			// Next read should start with \n