Bug 651956: Text tool misremembers point size upon reloading file

When setting the unit of a property shared with a gimp_prop_size_entry,
a conversion is applied to the corresponding size property (to preserve
size_entry's ref-value), but the conversion risks to change the size
property already updated.

To update, at the same time, size and unit, it is better to start updating
size_entry's unit in order to trigger the useless conversion on the stale
size.

app/tools/gimptexttool.c

@@ -1029,6 +1029,10 @@ gimp_text_tool_connect (GimpTextTool  *text_tool,
 
       if (text)
         {
+          if (text->unit != text_tool->proxy->unit)
+            gimp_size_entry_set_unit (GIMP_SIZE_ENTRY (options->size_entry),
+                                      text->unit);
+
           gimp_config_sync (G_OBJECT (text), G_OBJECT (text_tool->proxy), 0);
 
           if (text->markup)