Target last attacker

[Armus]

Am I missing something obvious? From what I read in the 1.51 patch notes, we were supposed to be getting a new shortcut key:

Added a new key (which is by default unmapped) that allows the player to target the last attacker. In general (if a player has no target already), his last attacker will be auto-targeted. This allows the player to switch to the last creature to do damage to him even if he's already targeted.

I can't seem to find this in the Keyboard Configuration settings. Has it actually been added?