UI: communicate external data autopack better in the UI.

Previously there was no way to see if autopack was enabled. Now the external
data menu has 3 entries instead of 2:

* Automatically Pack Into .blend (with checkbox to indicate autopack on/off)
* Pack All Into .blend
* Unpack All Into Files

Fixes T37608, includes modifications by Brecht from the original patch.

Reviewed By: brecht

Differential Revision: http://developer.blender.org/D118

release/scripts/startup/bl_ui/space_info.py

@@ -161,8 +161,18 @@ class INFO_MT_file_external_data(Menu):
     def draw(self, context):
         layout = self.layout
 
-        layout.operator("file.pack_all", text="Pack into .blend file")
-        layout.operator("file.unpack_all", text="Unpack into Files")
+        icon = 'CHECKBOX_HLT' if bpy.data.use_autopack else 'CHECKBOX_DEHLT'
+        layout.operator("file.autopack_toggle", icon=icon)
+
+        layout.separator()
+
+        pack_all = layout.row()
+        pack_all.operator("file.pack_all")
+        pack_all.active = not bpy.data.use_autopack
+
+        unpack_all = layout.row()
+        unpack_all.operator("file.unpack_all")
+        unpack_all.active = not bpy.data.use_autopack
 
         layout.separator()