[request] Make sure set_message() actually displays its given message (closes #3003425) The default automatic form sets a standard submit message as session data. However in some cases, such as the cancellation of a form edition, another message is intended to be printed on-screen. This patch makes sure that set_message() really scrubs all previous messages (and ids) from the request object and from the session data.

etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances