patch applied (ghc): Allow -package-id to override the default package shadowing semantics

[Duncan Coutts]

On Thu, 2009-09-17 at 05:49 -0700, Simon Marlow wrote:
> Thu Sep 17 05:15:10 PDT 2009  Simon Marlow <marlowsd at gmail.com>
>   * Allow -package-id to override the default package shadowing semantics
>   Ignore-this: 30d211e9989085f1de40552569b544b9
>   So that Cabal, if it wants, can use a more general algorithm to find a
>   consistent set of packages to use.

Thanks Simon.

As I said on #ghc yesterday, I think the significant thing is that it
means the semantics of package merging is simply Data.Map.union. Then
selecting a consistent subset is has to be done with the constraints of
the compiler in mind, but at least the basic merging is not
compiler-dependent.

Duncan