+Note [Runtime skolems]
+~~~~~~~~~~~~~~~~~~~~~~
+We want to give a reasonably helpful error message for ambiguity
+arising from *runtime* skolems in the debugger. Mostly these
+are created by in RtClosureInspec.zonkRTTIType. However at a
+breakpoint we return Ids from the CoreExpr, whose types may have
+free type variables bound by some enclosing 'forall'. These are
+UnkSkols, created ty TcType.zonkQuantifiedTyVar.
+
+These UnkSkols should never show up as ambiguous type variables in
+normal typechecking, so we hackily emit the debugger-related message
+both for RuntimeUnkSkols and UnkSkols. Hence the two cases in
+TcType.isRuntimeUnkSkol. Yuk. The rest of the debugger is such
+a mess that I don't feel motivated to clean up this bit.
+
+