[racket] Scribble change, especially affects `scribble/sigplan'

At Wed, 30 Mar 2011 22:41:20 -0400, Eli Barzilay wrote:
> Going back to the copyright issues -- is this a good time to get rid
> of the two offending latex files?

No. We have permission from CUP and SIGPLAN to distribute the style
files, so we need to add something that indicates our license to
distribute them.

(I expected the official copy of "sigplanconf.cls" to have a CC license
by now, so I'll check into that.)