pkgs/build-support/cabal: the configure-phase warning check can be
disabled by setting 'strictConfigurePhase' to 'false'

This is necessary for some packages, like dns, because cabal warns about
multiple versions of the same dependency being used, but the usage is fine,
actually, so we want the build to succeed. Packages that depend on 'doctest'
also have this issue <https://github.com/sol/doctest-haskell/issues/69>.
pkgs/top-level/release.nix: build the ghc 7.2.2 binary
haskell: don't provide 'binary' default, instead we override that
attribute in the compiler-specific package set

binary has become a core package in ghc 7.4.2, so we cannot easily build
stuff with our own version of it. (Least not without Cabal warning about
version conflicts in the build log.)