1. clear/* node_default and user_default now work.

2. in acc or rej/* you can now use (comma separated) prefixes as well as lists
of numbers for things like *_dxcc, *_itu and *_cq (eg: by_dxcc ve,w); just
remember that countries like ve and w have lots of zones and itus!
3. Added all the clear/* commands to help and added some comments about 2.
4. All filters (including *_default ones) are now reinstalled on channels in
realtime, so changing a filter does NOT require a disconnect and reconnect
cycle anymore.