If jsf 1.2 methods of ExternalContext are called with a jsf 1.1 impl, by default it should call default ones

In jsf 2.0, it was added a way to wrap previous ExternalContext versions, so when new methods are called, the default ones provided by the implementation are called instead.

This problem is also found when it is wrapped jsf 1.1 ExternalContext implementations and they run on myfaces 1.2. This is very rare, but there are some rare cases like weblogic native portlet impl.

The idea is do something very similar to FacesContext way to deal with getELContext: use a private ThreadLocal variable to hold the default instance for the current request. Then, FacesContextFactoryImpl set this variable.