SL Backcompat Plan:

*** 0.04006 mode

* get custom content from un-singularized classes in _load_external, with an
  appropriate comment that it's during upgrade only, for both static and
  dynamic schemas

* make use_namespaces the default, and upgrade to it properly

*** Catalyst Helper

* Add 'upgrade=1' option that upgrades from both old S::L and old helper,
  whichever or both.
* Warn when old helper output or 0.04000 S::L output is detected, that refers to
  the upgrade option.

Release dev S::L, announce to catalyst, dbic lists and #catalyst that testing of
backcompat mode is needed, wait 2-3 weeks, then release 0.05000.