Allow TransactionFactory::create() $version argument to be null, and change it to the default whenever this is the case. People may wish only to pass inputs/output.
Allow TransactionFactory::create() $version argument to be null, and
change it to the default whenever this is the case. People may wish
only to pass inputs/output.

blocktrail/bitcoin-php,Bit-Wasp/bitcoin-php,afk11/bitcoin-php,afk11/bitcoin-php,Bit-Wasp/bitcoin-php