channel_modes(): get rid of the trailing space
also make the *pbuf check work like it should
(don't call IsMember another time if we already
gave one parameter)
simplify a bit more, update comments
addition to +i. As before, a restrictive mode must be in
place at /invite time for the invite to have an effect;
+r does not count as a restrictive mode if the user is
logged in; +l and +j always count as restrictive modes to
allow for cases where they would allow join at /invite
time but not when the user tries to join.
