Cabal check warns about ill-specified dependencies

[guest]

Packages that get listed here:  http://hackage.haskell.org/packages/archive/preferred-versions

Get special treatment from cabal-install. It would help package authors if 'cabal check' could warn about version ranges, especially for packages listed in the preferred-version file.

For example, if the .cabal file just mentions package FOO and preferred-versions asks for FOO < X, then the author might not be aware that some people might expect to use FOO >= X. It would be nice to let the author know that they need to say, FOO == Y.* or FOO > A && FOO < B.

This is particularly important for base, where lacking an upper bound leads to bad build behavior.

This should probably be implemented in the Cabal library.