Don't reject ACL patterns without %u or %c, just warn.

Using `pattern blah/#` is a legitimate method of getting a global ACL.
We shouldn't be changing behaviour in a fixes release.

ChangeLog.txt

@@ -16,8 +16,8 @@ Broker:
   Closes #851.
 - Fix problem opening listeners on Pi caused by unsigned char being default.
   Found via #849.
-- ACL patterns that do not contain either %c or %u are now rejected. Closes
-  #209.
+- ACL patterns that do not contain either %c or %u now produce a warning in
+  the log. Closes #209.
 - Fix bridge publishing failing when per_listener_settings was true. Closes
   #860.
 - Fix `use_identity_as_username true` not working. Closes #833.

src/security_default.c

@@ -280,11 +280,9 @@ int add__acl_pattern(struct mosquitto__security_options *security_opts, const ch
 	}
 
 	if(acl->ccount == 0 && acl->ucount == 0){
-		log__printf(NULL, MOSQ_LOG_ERR,
-				"Error: ACL pattern '%s' does not contain '%%c' or '%%u'.",
+		log__printf(NULL, MOSQ_LOG_WARNING,
+				"Warning: ACL pattern '%s' does not contain '%%c' or '%%u'.",
 				topic);
-
-		return MOSQ_ERR_INVAL;
 	}
 
 	if(security_opts->acl_patterns){