chm_hidden modes are not seen if you oper up after joining

[jesopo]

if you don't oper up before joining a channel with a chm_hidden mode on it, you won't get told about it until you run /mode manually, and on irssi you actually have to /cycle.

[jesopo]

the solution i propose for this is sending :server MODE #chan +foo for any channels with chm_hidden modes when a user opers up. this will involve sending potentially redundant MODEs if a user deopers and reopers; I guess we could track if they either joined a channel as oper or have opered since a chm_hidden mode was set, but that seems painful for no real benefit