new cython modules for crypto++ and secp256k1 ecdsa support.
default to secp256k1 ecdsa module, support for crypto++ as well.

TX.verify1: pass data rather than hash (needed for crypto++ to work).
BlockDB.scan_block_chain: better handling of truncated blocks.bin.
verifying_machine.check_one_sig: verify1 protocol change.
code reduced to verify-only support, updated & tested.
use coro.ssl.openssl module rather than ctypes.

also: code reduced to verify-only.
feed_block: prepare for conditional tx verification.
support for crypto++ & secp256k1 [needs probe support].

updated cython required version.