get the operating system from within the OperatingSystem class, and cache the result

git-svn-id: svn://svn.icculus.org/fs2open@10727 387891d4-d844-0410-90c0-e4c51a9137d3
move mod validation into the OperatingSystem class as well

git-svn-id: svn://svn.icculus.org/fs2open@10728 387891d4-d844-0410-90c0-e4c51a9137d3
Don't parse bsp trees of non-colliding submodels.

git-svn-id: svn://svn.icculus.org/fs2open@10729 387891d4-d844-0410-90c0-e4c51a9137d3
Trunk sync r10729.

git-svn-id: svn://svn.icculus.org/fs2open@10730 387891d4-d844-0410-90c0-e4c51a9137d3
Initialize bay_arrive_speed_mult and bay_depart_speed_mult.

git-svn-id: svn://svn.icculus.org/fs2open@10731 387891d4-d844-0410-90c0-e4c51a9137d3