Make channel-specific plugin databases also network-specific.

[progval]

Currently, Limnoria supports channel-specific plugin databases, but channels with the same name on different networks are considered the same.

This should change.

This can probably be done in a backward-compatible way by looking for the old path (network-unaware) if the new path (network-aware) does not exist.

It may be possible to do this in a forward-compatible way by using a hard-link, but it's going to be a mess if there are two channels with the same name