Fix automatic attack for "Conquer City".

Fix automatic attack for "Conquer City".

The "Conquer City" action is an attack action. It is city targeted.

A potentially legal attack action should pop up the action selection dialog
if the popup_attack_actions client option is set or if another interesting
action is possible. If the "Pop up attack questions" is unset and no other
interesting action is possible the client should order the conquest without
asking the user.

Make the client able to order city targeted actions (like "Conquer City")
without asking the user.

Reported by wotan <wotan>
Debugged by Christian Knoke <chrisk>

See bug #25336

git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@34945 a0f10bec-cc02-0410-94fc-a9cfff90b4cd