Fix many bugs with the Symbols menu (when run with -d argument).

The Symbols menu is now fully useable.
A much more complete dsy file is included, called combined.dsy.
Generate the Symbols then use the combined.dsy file to identify far more functions.
You have to generate the symbol map FIRST or you can't use any .dsy files. It doesn't really make sense to use a .dsy file first then generate the symbol map. Anyway, it's nothing to do with my changes. But I can try to rename the Use Signature File item to something clearer.