This change set makes sure that if there is a tx with the same txid as a
previous tx in the block, the tx is marked as a duplicate and invalidated.
This change set is not backward compatible and so a new application
capability is introduced.

Change-Id: Ia1490079d716c5d51b23af0765bffed27b9b843c
Signed-off-by: Alessandro Sorniotti <ale.linux@sopit.net>