Changes to ghc

Changes to ghc:
commit cb8a63cb61af3cbc871b73071c6b894780f04cc5
Author: Joachim Breitner <mail@joachim-breitner.de>
Date:   Fri Feb 21 10:57:34 2014 +0100

    Major Call Arity rework

    This patch improves the call arity analysis in various ways.

    Most importantly, it enriches the analysis result information so that
    when looking at a call, we do not have to make a random choice about
    what side we want to take the information from. Instead we can combine
    the results in a way that does not lose valuable information.

    To do so, besides the incoming arities, we store remember "what can be
    called with what", i.e. an undirected graph between the (interesting)
    free variables of an expression. Of course it makes combining the
    results a bit more tricky (especially mutual recursion), but still
    doable.

    The actually implemation of the graph structure is abstractly put away
    in a module of its own (UnVarGraph.hs)

    The implementation is geared towards efficiently representing the graphs
    that we need (which can contain large complete and large complete
    bipartite graphs, which would be huge in other representations). If
    someone feels like designing data structures: There is surely some
    speed-up to be obtained by improving that data structure.

    Additionally, the analysis now takes into account that if a RHS stays a
    thunk, then its calls happen only once, even if the variables the RHS is
    bound to is evaluated multiple times, or is part of a recursive group.