In GimpAction, instead of connecting the action-history log
function to the action's "activate" signal as a user-provided
handler, call it directly from the default handler.

In subclasses of GimpAction, chain to the parent's activate()
function before emitting the "selected" signal, so that we always
log the action in the history before responding to it.

This allows us to avoid the hack in commit
6544ce43.

(cherry picked from commit 114d4951)