Fix bug #4687: session log gramplet - overzealous l10n of signal names breaks clickable link handlers

* No longer translate "link_type" passed to GuiGramplet.link,
this is an internal constant name never exposed to the user.
* Add a warning to GuiGramplet.on_button_press, in case an unknown link type
is encountered during the event processing
* Applied changes to my patch as suggested during the CR by dsblank



svn: r16714

src/gui/widgets/grampletpane.py

@@ -676,6 +676,8 @@ class GuiGramplet(object):
                                                      'attribute_match', 
                                                      handle)
                     return True
+                else: # overzealous l10n while setting the link?
+                    warn( "Unknown link type " + link_type, RuntimeWarning, 2)
         return False # did not handle event
 
 class GridGramplet(GuiGramplet):