activate XGrabServer again

This patch fixes a small problem which only rarely occurs. If a
window is opened only for a very short time and closed right away, in
some circumstances the frame around it stays opened. It looks like
Window Maker doesn't get the destroy message. The XGrabServer call was
commented in the code so I activated it again which seems to prevent this
from happening. I think it actually make sense since the ungrab calls are
used anyway in the following code.

src/window.c

@@ -612,7 +612,7 @@ WWindow *wManageWindow(WScreen *scr, Window window)
 	Bool raise = False;
 
 	/* mutex. */
-	/* XGrabServer(dpy); */
+	XGrabServer(dpy);
 	XSync(dpy, False);
 	/* make sure the window is still there */
 	if (!XGetWindowAttributes(dpy, window, &wattribs)) {