msys-gzip: Introduce our own package which upgrades to v1.6

This version supports deterministic compression/decompression, see
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=647522.

Signed-off-by: Thomas Braun <thomas.braun@byte-physics.de>
Merge pull request #17 from t-b/msys-gzip

msys-gzip: Upgrade to 1.6