+PH/15 Diagnose a filter syntax error for "seen", "unseen", or "noerror" if not
+ not followed by a command (e.g. "seen endif").
+
+PH/16 Recognize SMTP codes at the start of "message" in ACLs and after :fail:
+ and :defer: in a redirect router. Add forbid_smtp_code to suppress the
+ latter.
+