Suppress GUI shutdown crashes(#937, #172)

This is not really a solution, but kind of narrowes down the problem.
Our GUI uses an obsolete C-ish approach at releasing resources at
several points. This is probably a left-over from earlier days.

Especially since we started out with libGDL without C++ wrappers.
And at that time, we didn't use smart-pointers, as we should do,
but we tried to do things manually, which is an approach which never
works in an event driven and condition based environment. Goto fail.


Here I just commented out the manual clean-up code from several dtors.
The real solution would be not to allocate these resources through
the raw C calls at first place, but rather use the mm-wrappers
and leave it to them to unwind at the right moment.

TODO:

- scan the GUI code for *every* instance where we still muck around with gobjects
  and either replace that by a mm-wrapper, or wrap it in a smart handle.
- make sure that *all* dtors are either empty, or really airtight and EX_FREE

src/gui/workspace/panel-manager.cpp

@@ -62,12 +62,16 @@ PanelManager::PanelManager(WorkspaceWindow &workspace_window) :
 
 PanelManager::~PanelManager()
 {
+    ///////////////////////////////////////////////////////TICKET #195 : violation of policy, dtors must not do any work 
+    ///////////////////////////////////////////////////////TICKET #172 : observed as a reason for crashes when closing the GUI. It was invoked after end of main, when the GUI as already gone.
   
+#if false /////////////////////////////////////////////////TICKET #937 : disabled for GTK-3 transition. TODO investigate why this logic existed...    
   for(int i = 0; i < 4; i++)
     if(dockPlaceholders[i])
       g_object_unref(dockPlaceholders[i]);
       
   clear_panels();
+#endif    /////////////////////////////////////////////////TICKET #937 : (End)disabled for GTK-3 transition.
 }
 
 void
@@ -311,6 +315,8 @@ PanelManager::remove_panel(panels::Panel* const panel)
 void
 PanelManager::clear_panels()
 {
+    ///////////////////////////////////////////////////////TICKET #195 : this whole approach smells like an obsolete "C-style" approach.  We should strive to let the runtime system do such stuff for us whenever possible, eg. by using smart pointers
+  
   list< panels::Panel* >::iterator i;
   for(i = panels.begin(); i != panels.end(); i++)
     delete *i;