Update the settings for a poll, or add a new one.
Must be called with a topic specified in the URL.
The user must have poll_edit_any/poll_add_any permission
for the relevant action. Otherwise they must be poll starter
with poll_edit_own permission for editing, or be topic starter
with poll_add_any permission for adding.
In the case of an error, this function will redirect back to
EditPoll and display the relevant error message.
Upon successful completion of action will direct user back to topic.
Accessed via ?action=editpoll2.