[OPTIM] insert: slightly optimize the non-duplicate case
[OPTIM] insert: slightly optimize the non-duplicate case

Most inserted data will not be duplicates. It's better to optimise
for such a case by merging the comparison, eventhough this adds 2
unused assignments in the duplicate path.

sociomantic-tsunami/ebtree,sociomantic-tsunami/ebtree,haproxy/ebtree