Don't install git-gui

This fixes a few issues observed on some platforms:

* Don't require `tcl/tk` to be installed and configured on a platform. This also disables `git-gui` which is really not needed on headless build slaves.
* Ensures `gettext` is installed. This packge's `msgfmt` binary is required by configure/compile process.

/cc @opscode-cookbooks/release-engineers