Add '-k' feature from FreeBSD plus GNU gzip compatibility fix
This patch adds some features/improvements from FreeBSD:
- Add a '-k' option which does not remove input file, like bzip2(1) do.
- Use better representation of 'S:' by expanding ':' to '.suffix'
- Simulate GNU gzip(1) behavior where full filename is being output in
verbose mode when doing recursive.
If someone have commit access liked the patch, you can also find the
patched checked out version on leaf's /home/delphij/build/gzip.
Note, that I have intentionally left .Dd in gzip.1 intact, because I do
not know the exact date or wheather it would hit the tree. When
committing the code please consider bumping the date.