Added --mouse option to enable mouse tracking, and fixed bug in assumption that nv is not null.
Added --mouse option to enable mouse tracking, and fixed bug in assumption
that nv is not null.


git-svn-id: 23b6355f2bb369032457de4eb5f713ee134f73a8@8073 16af8721-9629-0410-8352-f15c8da7e697

joevandyk/osg,joevandyk/osg,joevandyk/osg,joevandyk/osg,joevandyk/osg