Exploring Zope code finally revealed what we needed in the
code, to allow removing the "trick".
It's a "trick" because we have no real reason to call
again the __init__ method of a metaclass: it's nicer to
understand what we need to do and to do it explicitely.

In this case, the __get__ slot was missing after the __bases__
assignement (bases are recomputed and as a result __get__ is
null'ed), and there is a method exposed in Zope's ExtensionClass
to do exactly this and only this.

The InitializeClass calls are included because
ExtensionClass.__init__ calls __class_init__, which sets correctly
roles and security on the class.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@39752 20353a03-c40f-0410-a6d1-a30d3c3de9de