* dlmalloc.c: New file. Port of Doug Lea's malloc

* dlmalloc.h: Ditto.
* Makefile.in: Add support for MALLOC_DEBUG
* config.h.in: Ditto.
* winsup.h: Ditto.
* configure.in: Add --enable-malloc-debugging option.
* configure: Regenerate.
* debug.h: Include declarations for debugging malloc.
* tty.cc (grantpt): Fix definition.
(unlockpt): Ditto.

winsup/cygwin/debug.h

@@ -9,6 +9,8 @@ details. */
 #ifndef MALLOC_DEBUG
 #define MALLOC_CHECK do {} while (0)
 #else
+#include <stdlib.h>
+#include "dlmalloc.h"
 #define MALLOC_CHECK ({\
   debug_printf ("checking malloc pool");\
   (void)mallinfo ();\