While preparing ERP5 upgrade for my customer, I noticed that their patch bt5 defines several XXX_init Python Script to customize behavior and I thought it would be great to have an afterClone-like getTypeBasedMethod for init_script too and thus this would get rid of many patched Portal Types.

Furthermore, there are several commits in erp5.git adding XXX_init Python Script doing the same thing so it seems I'm not the only one who could benefit from such feature.

Unit Tests passed with these changes.