Two fixes for package-scoped global variables:
* for left-hand-sides, only use foo._ syntax, not (foo._||foo._$get()),
  which leads to a syntax error. Note that the current code leads to
  static code not being executed in IE8 if a global variable is assigned
  before it is ever read.
* global constants with an initializer of some Object type were
  mistaken for a property definition, resulting in an undefined value.
Adding RequireJS's domReady module / plugin, because it seems
Ext.onReady() does not work when Ext is loaded via RequireJS.
fixing loadClass[es](): they didn't return the function as module value!
On the fly, extended loadClass() by the callback being optional. Without
a callback, it tries to retrieve an already loaded class synchronously.
re-introducing some Jangaroo meta-classes for backwards-compatibility