decoderawtransaction: show gettxout info of inputs of raw transactions

When decoding raw transactions, it is useful to have information about
the inputs beyond their txid and vout. If this information is available,
this patch adds it to the json output of decoderawtransaction.

On IRC recently I was explaining to somebody how to interpret the output
of decoderawtransaction. It was a pain to tell him to go look up each of the
input txouts separately, when I knew they were all unspent and sitting in
his wallet, so his bitcoind had ready access to them.