MDL-38654 add full $CFG->gdversion backwards compatibility for now

lib/db/install.php

@@ -327,6 +327,9 @@ function xmldb_main_install() {
     set_config('themerev', time());
     set_config('jsrev', time());
 
+    // No admin setting for this any more, GD is now required, remove in Moodle 2.6.
+    gdversion('gdversion', 2);
+
     // Install licenses
     require_once($CFG->libdir . '/licenselib.php');
     license_manager::install_licenses();

lib/db/upgrade.php

@@ -1758,7 +1758,7 @@ function xmldb_main_upgrade($oldversion) {
 
     if ($oldversion < 2013032200.01) {
         // GD is now always available
-        unset_config('gdversion');
+        set_config('gdversion', 2);
 
         upgrade_main_savepoint(true, 2013032200.01);
     }