fixed #1980 -- missing pass-through
possible fix for #1981
small optimizations

user.isOnline works with an array of uids
do not make 2 trips to db to get main post and first 10 posts
send uids to isOnline in messaging
crash fix
reverted main post change, breaks indices
doing it properly this time

mainPost always has index 0
further fix to #1957
sacrificing a goat to ensure this doesn't come back to bite me
fixed #1981