Weapon Object Radius is Ignored for Ship-Weapon Collision Checks

Migrated from Mantis http://scp.indiegames.us/mantis/view.php?id=3169

Originally submitted by @z64555
> This is a phenomenon most notable in mods where munitions have a significant difference in size from FS2 weapons (Think big bullets and missiles here). All weapons are treated as if they have the same size, regardless of their representative .pof radius and/or @Laser Head Radius.
>
> Mod a laser weapon to have a significantly large Head Radius (we'll go with 5.0)
> Mod a laser weapon to use a .pof, presumably that of a sphere of radius 5
>
> Shoot a standard laser at a dummy ship target and find a point where it'll *just* miss hitting its hull. The shield shouldn't interact with it.
>
> Switch to the modded lasers and perform the same test. What *should* happen is that the larger size of the weapons would trigger a collision, and thus impact the shield and/or hull.