Refuse to allow clients to PART channels

Some irc clients (notably pidgin, empathy, and other IM clients with an IRC functionality) deal poorly with irc proxies. Closing a window, or even disabling an account, may result in a channel PART message being sent, largely defeating the purpose of ctrlproxy.

It would be very nice to be able to tell ctrlproxy "Do not allow clients to part channels", and the provide a ctrlproxy-specific method to part the channel intentionally.

This might apply to all channels, or simply to channels that ctrlproxy has been told to auto-join, since there's an implicit logic that automatically joined channels should be persisted.

Another factor in this is related to multi-channel: If multiple clients are connected to ctrlproxy, and one client PART's a channel, the other client may still want to have that channel open.

One potential approach for dealing with this could be to have a "reference count" of how many clients are using a particular channel, and then only forward the PART to the real IRC server when the channel reference count is zero. This could also provide an easy way to implement the aforementioned functionality, by adding an additional reference count for ctrlproxy "holding" the channel open.

The harder problem would probably be to avoid sending replicated messages to clients that are not participating in a given channel...