[AD] HEADER_HACK

[Jason Wilkins <fenix@xxxxxxxxxx>]

I would like to propose another build "target" (like SCAN_EXPORT), but
call it something like HEADER_HACK, it would looke something like this in 
alconfig.h:

#if HEADER_HACK
   #ifndef HACKER_HEADER
      #error You must define HACKER_HEADER on the command line.
   #else
      #include HACKER_HEADER
   #endif
#elif SCAN_EXPORT
  .
  .
  .

HEADER_HACK could, theoritically, replace SCAN_EXPORT as a more general
target name, except I think SCAN_EXPORT is used elsewhere to control the
preprocessor.  I propose HEADER_HACK because it could be used by anyone
else who comes along and decides they want to fiddle with the headers to
generate something.

This is the only new thing i've had to add to allegro to support my
efforts to automatically generate a Microsoft Interface Definition
Language file and a friendly wrapper DLL for use with Visual Basic.

The other change was to some function arguments that are pointers to
functions which were not defined using AL_METHOD().

There where 6 places, mostly in the windows headers, where the pointer was
defined directly instead of using AL_METHOD().  I was defining these as
long int pointers because MIDL just hates pointers to functions (its such
a stupid compiler, it barfed out 6000 error messages because of all the
pointers to functions in allegro.h).

Lets see if I can remember what functions this affected, just in case
someone feels like fixing them before I make a patch.

set_window_exit_hook
_add_exit_func
_remove_exit_func
wnd_?_proc
set_directx_?
set_directx_?

I also found an extra semi-colon that gunked things up somewhere ^_^