Add options to keep/avoid reflink'ed file duplicates

[Fat-Zer]

It would be nice to have some options for reflinks to avoid them from listing in output. The options should behaves pretty much the same as options as those hardlinks counterparts (--keep-hardlinked and --no-hardlinked) but rely on reflink --is-reflink logic rather than inode number.

[SeeSpotRun]

Should be possible. I don't have much time at the moment but will try to get back to this in a few weeks.

[SeeSpotRun]

Two-and-a-bit years later...

Feel free to try out https://github.com/SeeSpotRun/rmlint/tree/feature/keep_reflinked

Main additional feature is that existing reflinks (above a configurable size) are identified prior to hashing. This should significantly speed things up if files are already reflinked.

When used in combination with -c sh:clone it will emit a shell script which, for existing reflinks, outputs
skip_reflink <orig> <clone>
for existing reflinks.