contextl fix

[Attila Lendvai]

Pascal,

darcs pull http://common-lisp.net/project/cl-dwim/darcs/contextl/

as far as i can see there was a missing dependency in the .asd as
reported by a cl-perec user. i couldn't reproduce it, but asdf has
this annoying habit of using file-system order unless the dependencies
specify otherwise...