sane ordering of args to eval_script().
sigpushonly flag support.
BadDER Exception. sane ordering of eval_script args.

moved verify-flags into verifying_machine.
pop_int: verify added only in the subclass.
check_pub: raise BadDER.
new bip62 exceptions.
sane ordering of eval_script args.
verifying_machine.eval_script - check_sigpushonly.