Fixed problem with missing denotations in polyDefDef

Problem was reported by @darkdimius. Test case will come in next commit.
Make self types always include a reference to the class

In a situation like

    class C { this: D =>
    }

the effective self type of the class is taken to be D & C.

Why? First, Scala 2.x does it that way. Second, it's needed to make the
FullParameterization transform go though.
Handle selftypes in FullParameterization

Adapt the transformation so that self types are handled correctly.