Initialize/create OGNL ValueStack before instantiating the Action

PicoContainer (http://www.picocontainer.org) needs access to the ValueStack in order to put together the container to resolve Type3 (constructor based) dependencies defined as constructor arguments. When instantiating, it will look through the tree of containers trying to resolve all dependencies. Since DefaultActionInvocation only initializes/creates the ValueStack after the action is created (createContextMap), PicoContainer will throw a NPE when accessing it.

Attached is the patch which initializes/creates the stack before createAction is called. Only pushing the action and actioninvocation onto the stack were moved out of the protected createContextMap method. I'm not sure what this means in terms of portability, but I see no problems.