Clear the tip acl when a node is released.

db/Node.pm.in

@@ -3754,7 +3754,10 @@ sub ClrTipAclUrl($)
     my $node_id = $self->node_id();
     
     DBQueryWarn("update tiplines set urlhash=NULL,urlstamp=0 ".
-		"where node_id='$node_id'");
+		"where node_id='$node_id'")
+	or return -1;
+
+    return 0;
 }
 
 # Stubs for calling "libTaintStates" common taint handling code

db/nfree.in

 #!/usr/bin/perl -w
 #
-# Copyright (c) 2000-2013 University of Utah and the Flux Group.
+# Copyright (c) 2000-2014 University of Utah and the Flux Group.
 # 
 # {{{EMULAB-LICENSE
 # 
@@ -488,6 +488,9 @@ foreach my $node (@freed_nodes) {
     $node->ClearBootAttributes() == 0
 	or $error++;
 
+    $node->ClrTipAclUrl() == 0
+	or $error++;
+
     #
     # If the node is a virtnode, force its state to SHUTDOWN. This is mostly
     # to avoid silly stated warnings for nodes that do not have a physical