Add command /saverequiredonconflicts to ask for saving even if there are conflicts in the file

Based on TortoiseSVN revision 24464

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Only subclass if the user data could be set

Based on TortoiseSVN revision 24465

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>