message: add OP_RETURN to list of imported opcodes since we use it
diff: @@ -7,7 +7,7 @@ import pdb
  import binascii
  from .mininode import *
  -from .script import CScript, OP_TRUE, OP_CHECKSIG, OP_DROP, OP_DUP, OP_HASH160, OP_EQUALVERIFY, OP_CHECKSIG
  +from .script import CScript, OP_TRUE, OP_CHECKSIG, OP_DROP, OP_DUP, OP_HASH160, OP_EQUALVERIFY, OP_CHECKSIG, OP_RETURN
  from .util import BTC
  # Create a block (with regtest difficulty)
  