Bug - Prevent players from entering towed vehicles.

- Fixed bug which allowed players to enter towed vehicles, allowing them
  to ghost through walls to gain access to modular bases.
- Added check to interupt the attaching of the tow if a player enters the
  vehicle during the attachment phase.
Merge pull request #4 from matt-d-rat/story/prevent-entering-towed-vehicles

Bug - Prevent players from entering towed vehicles.