refactor(Angular): add isPromiseLike helper function

This can be used internally to remove the repeating pattern of `obj && obj.then`. For now, I don't see a good reason to expose this in angular's public interface.

Conflicts:
	src/Angular.js

lib/promises-aplus/promises-aplus-test-adapter.js

@@ -2,6 +2,7 @@
 'use strict';
 
 var isFunction = function isFunction(value){return typeof value == 'function';};
+var isPromiseLike = function isPromiseLike(obj) {return obj && isFunction(obj.then);};
 
 var $q = qFactory(process.nextTick, function noopExceptionHandler() {});