Computer Player does not adhere to currently allowed buildings

[SirVer]

The computer player is not adhering to the Player::is_building_type_allowed. It only checks once for the valid building types in defaultai.cc::2138. This brings problems when scenarios activate or deactive buildings for the computer player.

The bug did not surface earlier because no scenario used this functionality so far and the allowed_buildings map packet is loaded before the computer player constructs it's allowed buildings cache. The allowed_buildings packet is likely going to be removed in build16, so computer player must learn to follow the rules.

This bug is easy to fix, the necessary changes are in mostly in defaultai.cc.

[SirVer (sirver)]

Released in build16-rc1