There is no need to create the graph step by step with only dependencies
already registered as far as the depth computation is propagated to all the
children.
Instead of searching level by level the nodes to iterate, it is faster to use
the sort of Python.
create_graph does not need to return its internal states but only the graph.
The ir.module activate and update method does not need to check for missing
dependencies because it is already checked at startup.
issue7466
review45211002
changeset 83757dc87808 moved the buttons from res to ir module but it missed
the migration of the model data to allow updates from previous databases
issue7186
review38031003
Changeset9bb9fe4cd312 modified the behaviour to mark them as not activated but
they should be marked as to remove so their data is correctly removed with the
install/upgrade wizard.
issue6019
review31691002
Cédric Krier