Attempt to make --x-initial-edge work for initial blocks with delayed assignments.

src:
	* V3Active.cpp (visit(AstAssignDly*, ...)): Mark new AstAssign as
	having been delayed originally.
	* V3AstNodes.cpp (AstAssign::dump): Created.
	* V3AstNodes.h (AstAssign): Add m_delayed and new accessor and
	dump functions.
	* V3Order.cpp (OrderVisitor): Add m_inInitial and m_wasDelayed.
	(iterateNewStmt): Blow away unused initial vertices.
	(visit(AstActive*, ...)): Don't ignore initials.
	(visit(AstNodeVarRef*, ...)): Add vertex for delayed assignments
	in initial blocks.
	(visit(AstInitial*, ...)): Created, to mark m_inInitial and call
	iterateNewStmt.
	(visit(AstAssign*, ...)): Created, to mark m_wasDelayed.
	(OrderVisitor): Set m_inIntial and m_wasDelayed in constructor.

test_regress:
	* t/t_initial_edge2.v: Clearer commenting.
	* t/t_initial_edge2_bad.pl: Created for non-delayed assignment case.
	* t/t_initial_edge2_bad.v: Created for non-delayed assignment case.