Do not rely on strict handling in setEdge (#31)

Previously setEdge relied on "use strict" for handling args. It turns
out the PhantomJS doesn't handle "use strict" under some conditions,
causing code that used setEdge to fail. This change makes the argument
work regardless of whether "use strict" is used or not. There isn't a
good way to test this, unfortunately...

lib/graph.js

@@ -304,14 +304,9 @@ Graph.prototype.setPath = function(vs, value) {
  * setEdge(v, w, [value, [name]])
  * setEdge({ v, w, [name] }, [value])
  */
-Graph.prototype.setEdge = function(v, w, value, name) {
-  var valueSpecified = arguments.length > 2;
-
-  v = String(v);
-  w = String(w);
-  if (!_.isUndefined(name)) {
-    name = String(name);
-  }
+Graph.prototype.setEdge = function() {
+  var v, w, name, value,
+      valueSpecified = false;
 
   if (_.isPlainObject(arguments[0])) {
     v = arguments[0].v;
@@ -321,6 +316,20 @@ Graph.prototype.setEdge = function(v, w, value, name) {
       value = arguments[1];
       valueSpecified = true;
     }
+  } else {
+    v = arguments[0];
+    w = arguments[1];
+    name = arguments[3];
+    if (arguments.length > 2) {
+      value = arguments[2];
+      valueSpecified = true;
+    }
+  }
+
+  v = "" + v;
+  w = "" + w;
+  if (!_.isUndefined(name)) {
+    name = "" + name;
   }
 
   var e = edgeArgsToId(this._isDirected, v, w, name);