With the blocking modal_run(), the game's main loop is frozen while a
menu is open, so the flag's input-suppression and VM-pause checks are
unreachable. Quit requested during a modal is now handled by closing the
modal and letting it propagate through the main loop.
This removes font.h dependency from header files such as ags.h and
nact.h. After this, font.h must be explicitly included in order to use
font functions.
kichikuou