Redirect to search page when the original search yields no results, inspired by #71310.

#58086: Base directory is used when performing af 404 search
#58147: Infinite loop with Drupal 4.7 RC3

Thank you very much, tenrapid!

Minor refactoring of search404.module.

Fix for bug #41637. Instead of showing the results on the "file not found"-page, the user is redirected to a search page with a message telling the user what happened.

New feature: you can now tell search404 to jump directly to the resulting node if the search only yields one result.

Fixed a bug - the "Set Search 404 to be your default 404 page." was not checked when Search 404 was enabled.

Also, moved a else and elseif to conform to coding standards.