Don't generate a mask if there's a pending configure event for the window
since it's likely that the shadow will be very quickly discarded.
(I find that this speeds up resizing somewhat: shadow generation no longer
lags behind.)

Signed-Off-By: Darren Salt <linux@youmustbejoking.demon.co.uk>

Index: src/compositor.c
===================================================================
--- src/compositor.c	(revision 22242)
+++ src/compositor.c	(working copy)
@@ -819,6 +819,7 @@
     DisplayInfo *display_info;
     ScreenInfo *screen_info;
     XRectangle r;
+    XEvent ev;
 
     g_return_val_if_fail (cw != NULL, None);
     TRACE ("entering win_extents: 0x%lx", cw->id);
@@ -836,7 +837,8 @@
        - It's a window with a frame and the user asked for shadows under regular
          windows,
        - it's an override redirect window that is not shaped, not an argb and
-         the user asked for shadows on so called "popup" windows.
+         the user asked for shadows on so called "popup" windows
+       - there isn't a pending configure event for this window.
      */
 
     if (!(screen_info->overlays) &&
@@ -845,7 +847,8 @@
              screen_info->params->show_popup_shadow) || 
          (!WIN_IS_OVERRIDE(cw) && 
              (WIN_HAS_FRAME(cw) || !(WIN_IS_ARGB(cw) || WIN_IS_SHAPED(cw))) && 
-             screen_info->params->show_frame_shadow)))
+             screen_info->params->show_frame_shadow)) &&
+        !XCheckWindowEvent (display_info->dpy, cw->id, StructureNotifyMask, &ev))
     {
         XRectangle sr;