better bind, use native fn.bind if available

spec/suites/core/UtilSpec.js

@@ -49,13 +49,14 @@ describe('Util', function () {
 			var fn = sinon.spy(),
 				foo = {},
 				a = {},
-				b = {};
+				b = {},
+				c = {};
 
 			var fn2 = L.Util.bind(fn, foo, a, b);
 
-			fn2();
+			fn2(c);
 
-			expect(fn.calledWith(a, b)).to.be.ok();
+			expect(fn.calledWith(a, b, c)).to.be.ok();
 		});
 	});
 

src/core/Util.js

@@ -18,10 +18,17 @@ L.Util = {
 		return dest;
 	},
 
-	bind: function (fn, obj) { // (Function, Object) -> Function
-		var args = arguments.length > 2 ? Array.prototype.slice.call(arguments, 2) : null;
+	bind: function (fn, obj) {
+		var slice = Array.prototype.slice;
+
+		if (fn.bind) {
+			return fn.bind.apply(fn, slice.call(arguments, 1));
+		}
+
+		var args = slice.call(arguments, 2);
+
 		return function () {
-			return fn.apply(obj, args || arguments);
+			return fn.apply(obj, args.length ? args.concat(slice.call(arguments)) : arguments);
 		};
 	},