Update for ghc 7.8

Bumped the dependencies on base to 4.7, and called ```tagToEnum#``` on the expressions that used to be ```Bool```, but became ```Int#``` with GHC.Prim 0.3.1 (mostly ```geFloat#```s).  After applying @glguy 's fix in ```Angle.hs``` and making a couple small changes to repa-alrogithms (will send a pull-request for this soon), all examples build and run well for me.

I see there aren't many pull requests - sorry if here is the wrong place for this.  And aside from reading Jan Stolarek's [blog post](http://lambda.jstolarek.com/2013/08/ghc-gets-new-primops) and your GHC Trac [wiki page](https://ghc.haskell.org/trac/ghc/wiki/PrimBool) this is my first time to see / think about primops - I hope I didn't make any mistakes.