Renamed remove_unreferenced_vertices as delete_unreferenced_vertices.
Added routines for determining if an isosurface patch is a disk.
New version of check_disk.  Not yet tested.
Corrected coding error in compute_num_split in ijkisopoly.txx.
Corrected coding error in unmap_non_disk_isopatches.
  Call tri_vert.clear() and quad_vert.clear() before calling
    get_non_degenerate_quad_btlr();
Added loop to unmap_non_disk_isopatches to recheck all isopatches
  after unmapping any vertices.
Updated isovert_info to match new code in isodual3D.