gzip: Fix silent fallback to decompression

gzip: Fix silent fallback to decompression

Bug-Debian: https://bugs.debian.org/355809
Forwarded: http://www.zytor.com/pipermail/klibc/2016-January/003892.html

If the gzip utilities are built without support for compression,
they will always attempt to carry out decompression even if the
command name and options don't imply that.  Instead they should
fail with an explicit error in this case.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Gbp-Pq: Name gzip-fix-silent-fallback-to-decompression.patch