[PATCH] gnu: Add geiser-next.

[Christopher Allan Webber]

If you want to hack trying out guile-next, you can't use the geiser
package.  Fortunately, the git version of geiser supports guile-next /
2.2 / (2.1?) so, here's geiser-next!

Not sure if other people care enough to have a geiser-next package, but
since we're Guile based here, I figured other people might want to be
hacking trying things out with the latest and greatest.

 - Chris