FIX: MD3Loader, revive dead branch.
FIX: TargetAnimation - clarify doc on preconditions.
FIX: aiMatrix3x3::FromTo - move cross product into a branch to save it we can do it without it.
git-svn-id: https://assimp.svn.sourceforge.net/svnroot/assimp/trunk@530 67173fc5-114c-0410-ac8e-9d2fd5bffc1f