Remove debugging code which did a full tree walk on every window operation

Eliminate needless (and, it turns out, dangerous) call to ChangeGC on
    DestroyGCPrivate.
in cwSetWindowPixmap, check if the pixmap is the screen pixmap and disable
    the wrapper by setting the private to NULL.

composite/compwindow.c

@@ -27,7 +27,7 @@
 #endif
 #include "compint.h"
 
-#ifndef NDEBUG
+#ifdef COMPOSITE_DEBUG
 static int
 compCheckWindow (WindowPtr pWin, pointer data)
 {
@@ -151,8 +151,10 @@ compPositionWindow (WindowPtr pWin, int x, int y)
      *
     compCheckRedirect (pWin);
      */
+#ifdef COMPOSITE_DEBUG
     if (pWin->redirectDraw != (pWin->viewable && (GetCompWindow(pWin) != NULL)))
 	abort ();
+#endif
     if (pWin->redirectDraw)
     {
 	PixmapPtr   pPixmap = (*pScreen->GetWindowPixmap) (pWin);