Avoid functions.php from ever being treated as a page template. fixes #16689.

git-svn-id: http://svn.automattic.com/wordpress/trunk@17539 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/theme.php

@@ -181,6 +181,9 @@ function get_page_templates() {
 			if ( false !== strpos($basename, '/') )
 				continue;
 
+			if ( 'functions.php' == $basename )
+				continue;
+
 			$template_data = implode( '', file( $template ));
 
 			$name = '';