dix: Fix wrong cursor refcount.

Calloc cursor struct to ensure devPrivates are zeroed out and don't
        increase the refcnt for devices automatically when allocating a new
        cursor. Use new DeviceIsPointerType() to detect if device is a pointer
        _before_ device has been activated and can thus be identified and set
        up grab functions accordingly. This way we can increase the refcnt
        when we get a pointer grab.

include/extinit.h

@@ -142,6 +142,11 @@ IResetProc(
 	ExtensionEntry *       /* unused */
 	);
 
+Bool
+DeviceIsPointerType(
+        DeviceIntPtr dev
+        );
+
 void
 AssignTypeAndName (
 	DeviceIntPtr           /* dev */,