added support for relay flag in version command (BIP0037)

I added support for the relay flag (fRelayTxes in Satoshi) in the version command.  This was added as part of BIP0037.  The Satoshi client (0.8.6) does not currently send this flag but it does respect it.  When set to false the Satoshi client will suppress the relaying on transactions until a bloom filter is set.

This is especially useful for building lightweight clients such as SPV only clients or backend clients that proxy off of bitcoind.