That change forced $output.extra_files_path to be the same thing as $output.files_path. See rational in changeset.
Some datatypes however consume this path when generated metadata - post d781366 these datatypes would be accessing the wrong directory. This fixes them.
The suggested best practice I would put forward is $input.extra_files_path and $output.files_path. $output.extra_files_path redirects to $output.files_path for newer Galaxy versions (August 2014+) so that Galaxy configurations requiring this directory be in the jobs working directory work. Datatypes consuming dataset.extra_files_path for these outputs will be broken when used with $output.files_path for the August release of Galaxy - but if this changeset is back-ported to the October 2014 release then these types and tools will work going forward (without modification).
It can be verified that the older releases are broken with the following existing test (fixed with this changeset).
./run_functional_tests.sh -framework -id composite_output
John Chilton
d475080370