KIND_XXX becomes an enum, is_p2sh.
verify0: move some of this logic into script.py.
implement p2sh, rework eval_script.

dhash, rhash: local copies.
machine.dump: hex encode stack items.
verifying_machine:
  __init__: no prev_outscript arg.
  check_multi_sig:
    don't count matches, just detect one, then exit the loop. (some extra pubkeys are broken).
get_op_fun:
  translate bad opcodes into ScriptFailure
eval_script:
  now takes a 'lock_script' and an 'unlock_script'.
  check for p2sh and execute it.
  previous eval_script is now _eval_script.
_eval_script:
  use get_op_fun.
find txns of different flavors & test their verification.