[Nix-dev] We use GHC 7.10.1 by default

[Peter Simons]

Hi guys,

starting with commit d50fe49dede130ef76c613c3827290dd7f21474c, the
default compiler in Haskell NG is GHC 7.10.1:

  $ nix-build -o /tmp/haskell "<nixpkgs>" -A haskellngPackages.ghc
  /nix/store/pwgwx7p0r262rz8v26rp1mjw1z6cj8vb-ghc-7.10.1

Have fun discovering all those new and exciting regressions, ICEs, and
library build failures that Nixpkgs now provides! ;-) If you don't want
to be involved in any of this, then you can still use the 7.8.4 compiler
at "haskell-ng.packages.ghc784.ghc".

Best regards,
Peter