Followup fix to mantis 2887 (from MageKing17)

no-collide ship classes would collide unless the no-collide flag was set
in the mission file

git-svn-id: svn://svn.icculus.org/fs2open/trunk@10989 387891d4-d844-0410-90c0-e4c51a9137d3
Fix mantis 2985 (from Yarn)

Fix float-to-int rounding errors in gr_[re|un]size_screen_pos

git-svn-id: svn://svn.icculus.org/fs2open/trunk@10990 387891d4-d844-0410-90c0-e4c51a9137d3