Added support for full database rebuild (from File menu).
If you were using previous versions of TkGutenBrowse, you must do this to access image and audio files.
Prior to this release, the URL's for non-text files were just plain wrong (my fault, not Project Gutenberg's). Updating the database adds new entries, but does not fix old ones. Rebuilding the database takes a little longer, but will fix the old data as well as adding new entries.