Get rid of the expand tree operation.

We will be re-structuring the map/resolve identity operations so this will not
be required.
Got rid of special function parameter lookups.

This version will not compile.
Process function parameters as part of the function not the prototype.
Evaluate the RHS of an assign before the LHS.
WIP version of the combined map/resolve identity operation.
Only throw ExistsException if the identity check finds a different identity.
Allowed the automatic tree children processing to be stopped.

Put the accept function into the node class as it's always the same....
Misstep.
New GENERATE_ASSIGN macro. (Ugly...)
Combined varaible mapper and resolver works.