Restructured subroutines in mergesharp_merge.cxx.
Added checks for cubes with multiple isosurface vertices.
Added merging of pairs of cubes sharing an ambiguous facet.
Added option -out_select to output selected cubes.
Added option -out_sharp to output cubes containing corners or vertices.
Added select_ambig_to_connect_to_cube to ijkisopoly.txx but function
is not currently used by mergesharp.