drupal_set_message() only prints each message once by default

Previously, calling drupal_set_message() more than once with an identical message and type resulted in it showing the message each time. Changing the third parameter, $repeat, to FALSE would prevent this.

The new default value is now FALSE. If you are using drupal_set_message() as a debugging tool, this change can be confusing, as it will only print out each message once.