New cursor for mixed attack and capture order

[elexis]

When selecting a soldier and a siege engine, then the cursor will show the option to capture the building. Since most siege can't capture and since the order is wired to allow attacks, the result will be soldiers capturing and siege engines attacking.

There could be a cursor that detects that situation and changes the cursor to a new one (perhaps one that is the combination of the capture and attack cursor?).

Refs #3668.