updated drupal core to 7.51

includes/install.core.inc

@@ -809,6 +809,13 @@ function install_system_module(&$install_state) {
 
   variable_set('install_profile_modules', array_diff($modules, array('system')));
   $install_state['database_tables_exist'] = TRUE;
+
+  // Prevent the hook_requirements() check from telling us to convert the
+  // database to utf8mb4.
+  $connection = Database::getConnection();
+  if ($connection->utf8mb4IsConfigurable() && $connection->utf8mb4IsActive()) {
+    variable_set('drupal_all_databases_are_utf8mb4', TRUE);
+  }
 }
 
 /**