Prevent too old revision in form view

issue4211
review11551002
Don't restore text on many2one cleaning if not empty

The call to set_client in clean function could trigger a on_change that will
set a value to the current field. In such case, the previous text should not be
restored.

issue4238
review5701002
Add missing "Show revisions" and remove old "Go to" in doc

review8621002
Added search for pixmaps in site.USER_BASE

thanks to notzippy

issue4102
review12541002