proposal: reimplement Data.Graph.Inductive.Query.Dominators

Hi, (this is Trac ticket #2227, http://hackage.haskell.org/trac/ghc/ticket/2227) As pointed out at http://www.haskell.org/pipermail/haskell-cafe/2008-April/041739.html ff., Data.Graph.Inductive.Query.Dominators.dom is buggy. Furthermore, it's slow, so instead of submitting the quick fix from that thread, I've rewritten the module from scratch using a more efficient algorithm. The algorithm works by calculating the immediate dominators of the graph nodes first, so the patch also adds a function that returns those. It should be handy for flow graph analysis. Deadline for discussion ... is a week sufficient? That would be April 28th. regards, Bertram