External zip utility

This package adds a settings page to allow Moodle to use external command-line zip and unzip utilities rather than the PHP ZipArchive library. It's intended as a workaround to ZipArchive's inability to handle large zip files (see http://tracker.moodle.org/browse/MDL-34388 ).

I've only tested it in Ubuntu 12.04, so it may not work properly on other platforms, if their "zip" and "unzip" utilities have different command-line options or output formats. It almost certainly won't work in Windows, although it could with some work.

I welcome community contributions. If you've got a fix to make this plugin work on a different OS, or with a later version of Moodle, please send me a github pull request or a patch file.