Add WorldPanning flag for camera texture definitions.

- To make camera textures pan in world units instead of texture units, you
  can now add "WorldPanning" at the end of the cameratexture definition in
  ANIMDEFS, after the "fit" specification. e.g.

    cameratexture CAMTEX 128 128 fit 64 64 worldpanning
Add handling for +warp at the command line.

- Command-line console commands are executed before a level is entered, so
  trying to use +warp to position yourself at a specific location will not
  work. We now specially handle this command so that it does work.
- Fixed: AFSwordMissile::DoSpecialDamage had a unique prototype

  so it would never actually be called.
Merge branch 'maint'