Hello!

Recently I faced neseserity to uniq list in Guile. Surprised, that I
did not found ready solution, I decided to prepare it.

By analogy with sorting functions in `sort.c` I prepared
`uniq.c`(attached, but unfinished patch, lacking proper documentation).
But after I became curious, how slower would be Scheme version with
(set-cdr!). To my test (random list of small integers) it is about twice
as slow.

Is Guile Mainline interested in these routines, and if yes, does in your
opinion doubling execution speed worth resorting to C hacking?