Changed the writing out of tile imagery so that it only happens when the destination file format is not .ive.
Changed the writing out of tile imagery so that it only happens when the
destination file format is not .ive.

Added back in support for freeing un-needed tiles.


git-svn-id: 23b6355f2bb369032457de4eb5f713ee134f73a8@2849 16af8721-9629-0410-8352-f15c8da7e697

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