[racket] unsyntax in Scribble examples

At Mon, 15 Aug 2011 13:18:07 -0600, Matthew Flatt wrote:
> Forms like `racketblock' and `racketinput' have `RACKETBLOCK' and
> `RACKETINPUT' variants that use `UNSYNTAX' as the escae form, instead,
> but I never got around to `examples', etc. I think it would be better
> to add a keyword to specify an alternate escape form, so I'll look into
> adding that.

The `racketblock' and derived forms (including `examples') now support
an `#:escape' clause to pick an alternate escape identifier.