Issue #1617006 by ben.kyriakou: Add note to drupal_write_record docs saying not to use in update functions

includes/common.inc

@@ -6899,6 +6899,10 @@ function drupal_schema_fields_sql($table, $prefix = NULL) {
 /**
  * Saves (inserts or updates) a record to the database based upon the schema.
  *
+ * Do not use drupal_write_record() within hook_update_N() functions, since the
+ * database schema cannot be relied upon when a user is running a series of
+ * updates. Instead, use db_insert() or db_update() to save the record.
+ *
  * @param $table
  *   The name of the table; this must be defined by a hook_schema()
  *   implementation.