[gentoo-lisp] Ebuild for Racket 5.1

[Morgon Kanter]

Hey folks,

I noticed there wasn't yet an ebuild for the new version of Racket, so
I went ahead and made one. It's attached.

A couple changes besides just bumping the version number:
* Doesn't really seem like that makefile patch was required anymore (I
didn't need it), so I commented that out.
* The new Racket GUI system doesn't appear to include any of those
external libraries that the ebuild used to issue an "rm" for, so I
removed those bits from the ebuild (as well as the formerly
commented-out rm commands that were replaced by something different).

That's it for the changes, aside from a version bump.

Thanks,
-- Morgon