Small code cleanup by Falk Doering:

- PHP6 forward compatibility on accessing strings
- Better indenting, other cleanups on the plugin API file

include/db/mysql.inc.php

@@ -314,7 +314,7 @@ function serendipity_db_schema_import($query) {
 
     $query = trim(str_replace($search, $replace, $query));
 
-    if ($query{0} == '@') {
+    if ($query[0] == '@') {
         // Errors are expected to happen (like duplicate index creation)
         return serendipity_db_query(substr($query, 1), false, 'both', false, false, false, true);
     } else {