[AD] crash in allegro wip (cvs of today)

[Emmanuel A. <em...@ab...>]

This crash has been around for quite around, but I got to describe it
only today...

You get a sigsegv in linux (I don't know for other oses...) when
making a blit() call with a bitmap created in 8bpp (with
create_bitmap_ex) to a 16bpp screen.  I attach a modified version of
exmem.c to this email which demonstrates the problem.

Of course this problem does NOT occur with allegro 3.9.33.