[ab] lispbuilder-sdl-ttf updates

[Luke Crook]

I've updated lispbulder-sdl-ttf using the patches provided. Thanks Samium.

Please note that I have made modifications the to way that INITIALISE-DEFAULT-
FONT and WITH-OPEN-FONT work. Previously WITH-OPEN-FONT bound the symbol 
*DEFAULT-FONT* to FONT. But now it shadows the *DEFAULT-FONT* SYMBOL with a 
variable and binds the variable to FONT. So *DEFAULT-FONT* is set to FONT only 
within the scope of WITH-OPEN-FONT.

INITIALISE-DEFAULT-FONT will bind the symbol *DEFAULT-FONT* to FONT. INITIALISE-
DEFAULT-FONT will no longer complain if a FONT is already bound to *DEFAULT-
FONT* when the &OPTIONAL FREE parameter is T.

I have also added a new macro WITH-DEFAULT-FONT.

These changes should allow more than one FONT to be opened at any one time.

- Luke