Adds set-motion-debris-override sexp. This can be used to control the presence of motion debris, and overrides any user choice made through the -nomotiondebris commandline flag.


git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10445 387891d4-d844-0410-90c0-e4c51a9137d3