d_button_proc - Dialog procedure implementing a button object. Allegro game
programming library.
#include <allegro.h>
int d_button_proc(int msg, DIALOG *d, int c);
A button object (the dp field points to the text string). This object can be
selected by clicking on it with the mouse or by pressing its keyboard
shortcut. If the D_EXIT flag is set, selecting it will close the dialog,
otherwise it will toggle on and off. Like d_text_proc(), ampersands can be
used to display the keyboard shortcut of the button.