Enhancement - undo

- Removed obsolete undelete command.
- Removed obsolete undo command.
- Implemented new undo command as a call to the stubbed TDB::undo call.

src/TDB.h

@@ -61,6 +61,7 @@ public:
   int   commit ();            // Write out all tasks
   int   gc ();                // Clean up pending
   int   nextId ();
+  void  undo ();
 
 private:
   FILE* openAndLock (const std::string&);