gzip: zgrep takes -R option, but not -r or --recursive

[Paul Eggert]

Re <http://bugs.debian.org/225864>:

zgrep -R was never supported, and I don't think it actually worked.
In CVS gzip, -R now elicits a diagnostic, much as -r does:

  zgrep: -R: option not supported

This fix should appear in gzip 1.3.10.