Rework composite overlay window code to fix several resource management bugs.

The composite overlay window code had several misunderstandings of the
workings of the X server, in particular error handling paths would often
double-free objects. Clean all of this up by using resource destruction as
the sole mechanism for freeing resource-based objects.

composite/compint.h

@@ -155,6 +155,7 @@ typedef struct _CompScreen {
     VisualID			*alternateVisuals;
 
     WindowPtr                   pOverlayWin;
+    Window			overlayWid;
     CompOverlayClientPtr        pOverlayClients;
     
 } CompScreenRec, *CompScreenPtr;
@@ -172,6 +173,7 @@ extern DevPrivateKey CompSubwindowsPrivateKey;
 
 extern RESTYPE		CompositeClientWindowType;
 extern RESTYPE		CompositeClientSubwindowsType;
+extern RESTYPE		CompositeClientOverlayType;
 
 /*
  * compalloc.c
@@ -229,6 +231,25 @@ CompositeRegisterAlternateVisuals (ScreenPtr pScreen,
 Bool
 compScreenInit (ScreenPtr pScreen);
 
+/*
+ * compoverlay.c
+ */
+
+void
+compFreeOverlayClient (CompOverlayClientPtr pOcToDel);
+
+CompOverlayClientPtr
+compFindOverlayClient (ScreenPtr pScreen, ClientPtr pClient);
+    
+CompOverlayClientPtr
+compCreateOverlayClient (ScreenPtr pScreen, ClientPtr pClient);
+
+Bool
+compCreateOverlayWindow (ScreenPtr pScreen);
+
+void
+compDestroyOverlayWindow (ScreenPtr pScreen);
+
 /*
  * compwindow.c
  */
@@ -292,9 +313,6 @@ compCopyWindow (WindowPtr pWin, DDXPointRec ptOldOrg, RegionPtr prgnSrc);
 void
 compWindowUpdate (WindowPtr pWin);
 
-void
-deleteCompOverlayClientsForScreen (ScreenPtr pScreen);
-
 WindowPtr
 CompositeRealChildHead (WindowPtr pWin);