[ab] lispbuilder-sdl updates

[Luke Crook]

These are the latest lispbuilder-sdl updates.

1) Modified LOAD-IMAGE and SAVE-IMAGE to take a single 'filename' parameter 
instead of 'filename' and 'pathname' parameters. You can use CREATE-PATH if you 
need to merge 'filename' and 'pathame' prior to calling LOAD/SAVE-IMAGE.

2) Added the capability to read and write pixels from/to 3-byte surfaces.

-Luke