[AD] Using system mouse cursor

[Chris <kcat@xxxxxxxxxx>]

As brought up on allegro.cc:
http://www.allegro.cc/forums/view_thread.php?_id=390945

Would it be possible to create a function that would remove Allegro's 
mouse image and restore the system's default, while still updating the 
mouse_* vars? I ask because this would not only solve the problem of bad 
mouse handling (which results in mouse droppings) but also of wasted CPU 
time and the general hackyness of Allegro's interrupt-centric drawing 
code for it.

It should be rather easy to do this, shouldn't it? Just seperate the OS 
specific code to hide/show the system mouse pointer while over the 
window into a seperate vtable entry for the mouse driver, and use 
show_mouse(NULL) to disable Allegro's mouse renderer and still update 
the variables.

- Kitty Cat