fix typename decl asgn lookahead (resolves #49)

test/basic/port_typename.sv

@@ -0,0 +1,7 @@
+typedef wire b_t;
+module top(
+    input a [1:0],
+    input b_t b
+);
+    initial $display("%d %d %1d %1d", a, b, $bits(a), $bits(b));
+endmodule

test/basic/port_typename.v

@@ -0,0 +1,6 @@
+module top(
+    input [1:0] a,
+    input wire b
+);
+    initial $display("%d %d %1d %1d", a, b, $bits(a), $bits(b));
+endmodule