Situation with Zend Framework is this:
GitHub enables to link subproject, so Zend in the simpleinvoices respository is only link. The subproject is downloaded via git command with "--recursive" option. Zip file probably does not include this.
Anyway if you look at Zend-1.11 repository (https://github.com/dmelo/Zend-1.11/commits/master
) there was not update from 2012 so you can simply copy (or symlink) library from your older instalation.
Also SI updates are rather conservative and last commits were mostly about updating languages, but nobody make releases, so it’s ideal to use git to stay on actual development. If you work on Windows you can use very easy-to-use client from GitHub or others here http://git-scm.com/downloads/guis