Merge pull request #2

0891874 Add missing (MIN_)PROTO_VERSION definitions (Florian Schmaus)
2a2327c Remove coredefs import in messages.py (Florian Schmaus)
bc76c9f s/cStringIO/io for Python 3 compability (Florian Schmaus)
Encode -1 as OP_1NEGATE

See BIP62
Add 'addnode' RPC method
Use bitcoin.params instead of netmagic
My recent modifications
Frontport some old functions
Latest changes
Make all unit-tests work
Some cleanup
Some more work on bitcoin protocol messages