use display_graph_old for locale_deps, to show a bit more than nothing for cyclic graphs;

--- a/NEWS	Thu May 07 21:30:52 2015 +0200
+++ b/NEWS	Thu May 07 22:12:05 2015 +0200
@@ -87,7 +87,7 @@
 Options / Text Area).
 
 * Improved graphview panel with optional output of PNG or PDF, for
-display of 'thy_deps', 'locale_deps', 'class_deps' etc.
+display of 'thy_deps', 'class_deps' etc.
 
 * The commands 'thy_deps' and 'class_deps' allow optional bounds to
 restrict the visualized hierarchy.

--- a/src/Pure/Isar/isar_syn.ML	Thu May 07 21:30:52 2015 +0200
+++ b/src/Pure/Isar/isar_syn.ML	Thu May 07 22:12:05 2015 +0200
@@ -794,7 +794,7 @@
         Locale.pretty_locale_deps thy
         |> map (fn {name, parents, body} =>
           ((name, Graph_Display.content_node (Locale.extern thy name) [body]), parents))
-        |> Graph_Display.display_graph))));
+        |> Graph_Display.display_graph_old))));
 
 val _ =
   Outer_Syntax.command @{command_keyword print_term_bindings}