We'll re-enable it for MEMBERSHIP after e3, but this is the end of JOIN / PART for basic chat connections.
Moving forward, you will be required to request the MEMBERSHIP capability to receive JOIN and PART messages.
I have no idea how to do "Membership" in mIRC, it just seems like it will be overly complicated, and will break is op too, you'd have to do something like $hget(stream,$chan $+ ;moderators; $+ $nick) which you'd have to write a bunch of code for. Meh.
