(PR#11009) AI Hunts Own Units

<URL: http://rt.freeciv.org/Ticket/Display.html?id=11009 >

On closer inspection it appears the exact same bug appears in
assess_danger.  A player's own units will be considered dangerous when
assessing the danger for a city.  So, I committed the longer
is_player_dangerous patch to both branches.

However this may unveil new bugs because now cities aren't in continuous
danger.

I give this back to the AI people for further inspection.

-jason