[AD] aRts "pure virtual function call"

[jcugniere@xxxxxxxxxx]

Hello,

for quite some time now, allegro programs that use the arts sound driver under
linux have been crashing on exit with the error "pure virtual function call"
(I'm using allegro 4.1.12 right now). I just tried to find out why, and gathered
the following:

   1. The crash happen in arts.c, when _al_arts_exit() tries to call
arts_close_stream() or arts_free().
   2. If the program explicitely calls remove_sound() before exiting, the crash
doesn't happen.