[tz] [PATCH] Allow the gpg2 binary name to be overridden by the environment.

On some platforms, the gpg2 binary isn't actually called 'gpg2'; on OSX when you install GPG view Homebrew, it is just 'gpg'. This probably affects about three people on the planet, but noticed it when working on build scripts. --Matthew Donadio (matt@mxd120.com)