[options] gnc:warn when looking up old option names

the option lookup mechanism will dynamically translate option
names. warn the user if this takes place so that the report writer may
use new option names.

libgnucash/app-utils/options.scm

@@ -1749,6 +1749,9 @@ the option '~a'."))
                   (and name-match
                        (let ((new-section (car (cadr name-match)))
                              (new-name (cdr (cadr name-match))))
+                         (gnc:debug
+                          (format #f "option ~s/~s has been renamed to ~s/~s\n"
+                                  section name new-section new-name))
                          ;; compare if new-section name exists.
                          (if new-section
                              ;; if so, if it's different to current section name