minor enhancement to sub2ind.m and ind2sub.m

[John W. Eaton]

On  3-Jan-2008, Muthiah Annamalai wrote:

| minor enhancement to sub2ind.m and ind2sub.m to describe the formation
| of the linear index generation.
| -Muthu
| 
| Changelog entry
| 2008-1-3   Muthiah Annamalai <muthuspost at gmail.com>
|         general/ind2sub.m, general/sub2ind.m: add description of linear 
| index

I made this change.

Thanks,

jwe