Implemented findAndDelete.

Need for strange transactions with signatures in scriptPubkey.
See FindAndDelete in Bitcoin core.
Clean-up of CHECK(MULTI)SIG code.

Refactored some code and added enforcement of in-order
signature/pubkey satisfaction in MULTISIG
Bug fix: OP_CODESEPARATOR handling

Handling the case of co-separators in scriptSig but none in scriptPubkey.
Merge pull request #68 from lornap/checksig_update

Clean-up and update of CHECK(MULTI)SIG