Avoid TX to himself (without any change)
See this TX : http://gtest.duniter.org:10900/blockchain/block/4722
inso (key EHRCKQn8Tua39rRkMtvaj5tpFGcg7yeKyr8S9fJnVKwE) has sent one input to one output (same unitbase).
This is like pure noise ;) Why not to exclude such TX ?