#11 add option to not follow any symlinks but sum their readlink

[Charles Evans]

I often have links to partition image files of many gigabytes,
and many links to each of my distro's DVDnn.iso files, so
scanning a dir may take hours longer as each of 10 iso's is summed 10+ times. 400GB+ total extra.
An option to not follow any symlinks would fix this.
Another option to not follow any symlinks except those given on the command line
would be even better, but half the time I need these to be not followed either.
Symlinks not followed should have their readlink value summed instead
so the sig will change if the symlink is changed or replaced.
Thanks for a great program!