[AD] RGB structure

["Eric Botcazou" <ebotcazou@xxxxxxxxxx>]

The main header file (allegro.h) and the docs are not in sync about the RGB
structure:

*** quoted from allegro.h: ***
typedef struct RGB
{
   unsigned char r, g, b;
   unsigned char filler;
} RGB;

*** quoted from the docs: ***
typedef struct RGB
{
   unsigned char r, g, b;
} RGB;

Is this deliberate ?
What's the use of 'filler' ?

Other thing: I made an internal of black_rgb (defined as (RGB) {0, 0, 0, 0})
in my previous patch. It turns out that it is used in exactly two places:
the first one in allegro.c, the other one in keyconf.c . So I propose to get
rid of it.

--
Eric Botcazou
ebotcazou@xxxxxxxxxx