Add test condition for repository_tool.Target().add_target() custom data.
Verify that generated Targets metadata can contain custom data.
Regenerate '/tests/repository_data/' to include example of custom data.
Add test condition for custom data in test_updater.py.

The updater client may reference target information (including 'custom') by accessing the dictionary returned by updater.py.

Example:
target = updater.target('LICENSE.txt')
target['filepath']
target['fileinfo']['length']
target['fileinfo']['hashes']
target['fileinfo']['custom']