Log Message:
Update of racket ports to version 6.1.1. Coordinated with asau. Changes,
as per upstream changelog:
- Bug repairs and other changes noted in the documentation
- Changed use-before-definition to be an error instead of producing
 an #<undefined> value
- Removed the mzlib/class100 library

Also changed the racket port to use mk/jpeg.buildlink3.mk.