Initial code for detecting clock enables (not quite correct yet)

	* V3Gate.cpp (GateEitherVertex::iterateOutEdges): New method.
	(GateVarVetex::dotColor): Different color for clocks.
	(GateVisitor::m_statClockEn): New instance variable.
	(GateVisitor::findClockEn): New member function.
	(GateVisitor::visit(AstNetlist*)): call findClockEn after dedupe,
        first dumping the tree.
	(GateClockEnGraphVisitor): New class.