Comment out the "assert(is_tree(tree))" that I recently added to settreepair__tree(tree, treepair).
Add comments to explain the purpose and function of the two different stacks used by the evaluator.
Fix an inaccurate claim in a comment.
Rewrite directory_helper in terms wxWidgets instead of in terms of WIN32 API.
Replace "TRUE" with "true" because ther literal is used as a bool, not a BOOLEAN.
Change some #define constants into "const" values.
Refactoring: Change #define macros into inline functions.
Refactoring: Move the logic for pushing the macro_return continuation until after it's been confirmed that proc is defined.