filed the upstream bug as http://bugs.mysql.com/bug.php?id=67507 over 2 months ago, but there has been no progress ever since, so maybe it's time to start doing something on our side, since 5.5.29 still has it and incompatible clients keep spreading.
According to MySQL manual, the syntax SET OPTION was deprecated (even although it doesn't seem to produce any warnings in 5.5), and now in 5.6 it's removed. However, even current versions of mysqldump 5.1-5.5 keep using it, which makes mysqldump < 5.6 incompatible with server 5.6 / 10.0.
I think we should at least replace SET OPTION with SET in mysqldump 5.3/5.5 (or maybe even 5.1..5.5) to stop producing potentially incompatible versions.
Additionally, please consider if we should prolong life of SET OPTION syntax in 10.x in order to let patched clients a chance to replace the old ones. (This part is not indicated in Affected/Fixed versions as it's just a suggestion for future).