Fixed check for gzcat (and made it quieter).

[gdbentley]

No description provided.

[fredemmott]

What platform? cc @jwatzman

I wouldn't be surprised if this check is non-portable

[gdbentley]

It was failing for me on CentOS 7. I have a zcat but no gzcat. $cat ended up an empty string.

[jwatzman]

The 2>/dev/null is fine, but can we make the if test just check for !$cat? It wouldn't surprise me if we got different results (null vs empty string) on different platforms.

[gdbentley]

!$cat works for me.