AllegroCL 8.0 port

On the spur of the moment, I decided to try porting Graphic-Forms to AllegroCL 8.0. After a few hours work, I got all of the test programs running. It was fairly straightforward. These days, it seems that the main complication in porting Graphic-Forms is translating stdcall callback definitions into the vendor's particular FFI vocabulary. A CL whose dynamic FFI is a second-class citizen is likely to be a troublesome porting target, though.