The function assertDebuggingCalled() only expects one debugging message, where as a function can eventually send out more messages. We need to add some support for that.
Please fix lib/filestorage/tests/zip_packer_test.php around line 151 (look for TODO MDL-37429) with this issue.

The patch includes change of file packer API, the archive functions now include a new parameter that specifies what to do when file is invalid or missing. The zip packer may also create empty zip archive and later add files to it. All the new functionality is tested by unit tests. At the same time all obsolete hacks for PHP 5.2 were removed.