Added minimum size parameter to GtkWidgetClass->adjust_size_allocation.

This allows us to add a check before executing
->get_preferred_height_for_width() to ensure we always
request for at least the minimum required size (and lets
us remove the warning in gtkcontainer.c telling implementors
to do this check manually from thier container implementations).

gtk/gtkwidget.h

@@ -415,6 +415,7 @@ struct _GtkWidgetClass
                                            gint              *natural_size);
   void         (* adjust_size_allocation) (GtkWidget         *widget,
                                            GtkOrientation     orientation,
+                                           gint              *minimum_size,
                                            gint              *natural_size,
                                            gint              *allocated_pos,
                                            gint              *allocated_size);