gzip: add "--keep" option to keep original files unchanged

[Rodrigo Campos]

Hi,

Please keep me in Cc: since I'm not subscribed.

This path just adds the "--keep" option to keep original files unchanged. The
patch is very simple and I have tried it here (manpage and binary) and it seems
to work just fine.

I tried to respect the coding style (it is a very small patch, so hopefully I
did) and the commit format. But I wasn't sure how the commit format for this
patch should be. So please let me know which changes should I do.




Thanks a lot,
Rodrigo