It was in 1.8. It was even added in 14w06a as one of the features. http://minecraft.gamepedia.com/Boat#Trivia "If a mob is stacked on top of a boat in water (such as with the /summon command), the boat can be controlled by that mob."
Actually they HAVE been able to control boats. Due to the changes, mobs can no longer control boats. This is definitely a valid bug, especially since mobs can now manually get in boats without the /summon command. Someone please validate this report.
alon ran
It was in 1.8. It was even added in 14w06a as one of the features. http://minecraft.gamepedia.com/Boat#Trivia "If a mob is stacked on top of a boat in water (such as with the /summon command), the boat can be controlled by that mob."