MDL-39701 prevent filters before finishing 2.5 upgrade

This prevents problems with unsigned integers in MySQL 5.5

lib/weblib.php

@@ -1091,7 +1091,7 @@ function format_text($text, $format = FORMAT_MOODLE, $options = NULL, $courseid_
     }
 
     // Calculate best context
-    if (empty($CFG->version) or $CFG->version < 2010072800 or during_initial_install()) {
+    if (empty($CFG->version) or $CFG->version < 2013051400 or during_initial_install()) {
         // do not filter anything during installation or before upgrade completes
         $context = null;