fix(facades): fix splice semantics; add test

modules/angular2/src/facade/collection.dart

@@ -154,7 +154,8 @@ class ListWrapper {
   static List slice(List l, int from, int to) {
     return l.sublist(from, to);
   }
-  static List splice(List l, int from, int to) {
+  static List splice(List l, int from, int length) {
+    var to = from + length;
     var sub = l.sublist(from, to);
     l.removeRange(from, to);
     return sub;

modules/angular2/src/facade/collection.es6

@@ -193,8 +193,8 @@ export class ListWrapper {
   static slice(l:List, from:int, to:int):List {
     return l.slice(from, to);
   }
-  static splice(l:List, from:int, to:int):List {
-    return l.splice(from, to);
+  static splice(l:List, from:int, length:int):List {
+    return l.splice(from, length);
   }
   static sort(l:List, compareFn:Function) {
     l.sort(compareFn);

modules/angular2/src/facade/collection.ts

@@ -168,6 +168,9 @@ export class ListWrapper {
     return true;
   }
   static slice<T>(l: List<T>, from: int, to: int): List<T> { return l.slice(from, to); }
+  static splice<T>(l:List<T>, from:int, length:int):List<T> {
+    return l.splice(from, length);
+  }
   static sort<T>(l: List<T>, compareFn: (a: T, b: T) => number) { l.sort(compareFn); }
 }