haskell-scientific: add versions 0.1.0.1 and 0.3.2.1
haskell-scientific: there's no point in using 0.1.0.1, because it doesn't build with GHC 6.12.x either :-(
haskell-wreq: remove unnecessary overrides
Use attoparsec 0.10.x when building with GHC 6.x.

Newer versions depend on 'scientific', which this compiler cannot build.
haskell-defaults.nix: improve configuration for GHC 6.x
haskell-defaults.nix: move extensible-exceptions override into the right place
haskell-defaults.nix: override case-sensitive on GHC 7.2.2 to avoid build error
haskell-defaults.nix: fix hashable and case-insensitive builds with GHC 6.x
haskell-split: don't run the test suite with GHC 7.9.x to avoid infinite loop
haskell-defaults.nix: fix hashtables build with GHC 6.10.x