If in debug mode, prints the given error message and continues; otherwise redirects to the given error message image and exits; designed for a production gallery.
Parameters:
$errormessage
$errormessage:
string the error message to print if $_GET['debug'] is set.
$errorimg
$errorimg:
string the filename of the error image to display for production. Defaults to 'err-imagegeneral.png'. Images should be located in /zen/images .