create an option to skip files with more than X links

[ngrigoriev]

I had to use this great tool to deal with consequences of some stupid design decisions from the past, which resulted in many duplicate files stored. So many that for some of them the number of duplicates was in order of hundreds of thousands. I had to write a script to "compact" this tree and replace each group of X identical files with hardlinks. I wanted to make this tool fully automatic so it can be reused until the root cause of that mess is dealt with. It would be nice if I could tell the tool to ignore any files that point to inode with more than one hardlink (in my case they are already "processed"). I guess it could be a generic option to ignore inodes with more than specified number of hard links.