Correct getblock RPC handling and optimize.

The getblock RPC call should return a hex-encoded string of the block when
verbose is false instead of a BlockResult object with a Hex field set to
be compatible with the Sathoshi client.  This commit, along with a recent
commit to btcjson corrects this.

Also, while here, move code which only applies to verbose mode after the
call which handles the non-verbose logic.  This saves a few cycles since
the non-verbose logic doesn't need the extra information.