Provide configuration to turn off checksum validation

Recently, I have experienced a QuickFIX/J based application ignoring or rejecting messages with an invalid checksum (depending on the setting of the RejectGarbledMessage property). On the other hand, these messages featured the required structure for further processing.

So I have decided to provide an enhancement which allows the FIX Engine to process messages with invalid checksum as ordinary messages having passed validation. This enhancement will be provided as a configuration option controlled by the property ProcessMessageWithInvalidChecksum. By default, this property will be set to 'N' such that Messages with invalid checksum will be either ignored or rejected as before.

In particular, it will only be possible to set either RejectGarbledMessage or ProcessMessageWithInvalidChecksum to 'Y' for a specific session. If both properties are set to 'Y' at once, a ConfigError will be thrown.