reopen right now also based on [closed->assign] (in addition of [closed->new]), fix #2751
add Ticket::canReopen
remove only content from extraparamhtml
avoid right errors in timeline ajax
do not permit to reopen ticket if missing followup right, fix #2324

Drop strange assignation
Drop not used variables

Change cache prefix
Handle PHP 5.6

use sprintf for message

Prevent dropdown menu on self-service interface