Generalized phase control for GHC

[Max Bolingbroke]

> Ah -- Roman you mean you want to add a phase-ordering constraint at some time *other* than when you declare one or other of the phases.  Are you sure this is important?  It's an awkward addition because, like orphan instances, it means there's an interface file with perhaps-vital info which you might have no other reason to visit.

I've begun to think that we need some generalized framework for
gathering "orphaned" information since, as we discussed, the same
problem occurs with my new annotations system
(http://blog.omega-prime.co.uk/2008/07/05/compiler-plugins-for-ghc-weeks-three-and-four/)
if you wish to implement the ability to annotate identifiers from
other modules.

Max