Fix wxGTK wxDataViewRenderers' alignment handling

Don't apply alignment to native controls in SetAlignment() method, where
it may not be known yet due to column-to-renderer inheritance if
wxDVR_DEFAULT_ALIGNMENT is used (the default). Move such code to
GtkUpdateAlignment() (which was made virtual) in all renderers.

This fixes unintended right-aligning of columns with GTK+ 2 when default
alignment was used.

include/wx/dvrenderers.h

@@ -180,6 +180,10 @@ public:
     // wxDVR_DEFAULT_ALIGNMENT.
     int GetEffectiveAlignment() const;
 
+    // Like GetEffectiveAlignment(), but returns wxDVR_DEFAULT_ALIGNMENT if
+    // the owner isn't set and GetAlignment() is default.
+    int GetEffectiveAlignmentIfKnown() const;
+
     // Send wxEVT_DATAVIEW_ITEM_EDITING_STARTED event.
     void NotifyEditingStarted(const wxDataViewItem& item);