[form] fix #719285, due to multiple calls to restore_previous_post, by proper refactorings
* move __init__ code from FieldsForm to Form. Must behaviour here should actually be in the Form base class
* avoid buggy duplicated call to restore_previous_post
* move some code that was in the form renderer to the form'__init__ method (__redirectpath & __form_id hidden input handling))
* 'formvid' should now be specified on form selection, not on form rendering
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html