add more todo

Signed-off-by: Nico Schottelius <nico@kr.ethz.ch>

doc/dev/todo/post-1.3

@@ -3,6 +3,7 @@ Core:
    - support $__self = relative_type/object_id
    - .cdist
    - cache
+   - display changes if object cannot be merged to user
 
 Cache:
    Assume you want to configure stuff one host ("monitor node"),
@@ -31,3 +32,4 @@ Types to be written/extended:
       - regexp replace (can probably cover all?)
          -> aka sed.
    - __cron
+