master:
New shortcut "C-o k" to toggle the option "--known-types"...

In ack 2.0, the option --all is replaced with --known-types.

So in "Find with Ack" (C-o f a), while editing the search string in
the minibuffer, the current shortcut (C-o a) to toggle "--all" is
now useless if you use the later version of ack.