In the master branch, doCheck defaults to 'false', which means that no package
will change its hash unless its doCheck field is set to 'true' explicitly. In
the stdenv-updates branch, however, all Haskell packages have a default setting
of 'doCheck=true'. Once that branch has been merged, filtering doCheck is no
longer necessary.
Jailbreaks-cabal allows Nixpkgs maintainers to quick-fix builds of packages
that over-specify their version requirements by removing the version
restrictions of all dependencies from the Cabal file. Set
jailbreak = true
in the build expression to activate this feature.
