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.
Yes, but if I have already selected another dsy using the "Use Signature File" command and then pick the "Generate symbol map" command, why would the debugger use totaldb.dsy when I have already asked it to use the new dsy file I had selected?  It should have forgotten about totaldb.dsy and keep my latest selection in memory.