tigefa4u projects Trac

TracDiff:
* removed a few `print` statements
* clarified implementation notes for the `ArbitraryDiffModule`

TracDiff: refactored `ChangesetModule` and `DiffModule` to take advantage of [2086]: they now both inherit from the `AbstractDiffModule` class

TracDiff: merged with trunk (log:trunk#2039:2088)

Fix syntax error introduced in [2084].

Web-Admin: Mark `AbstractEnumAdminPage` as abstract.

* Make components inherit `implements()`, so that a subclass of a class implementing some extension point is also marked as extending that extension point.
* Allow marking component base classes as abstract.

Web-admin:
Web-admin:
* Use the `ez_setup` bootstrapper for setuptools.
* By default, tag the distributable with the SVN revision.
* Add notes that removing all options for a ticket field hides the field from the user interface.
* Allow changing the order/value of enum fields.

Remove duplicate import

Fix `trac-admin` tests for systems where plugins that add permission actions are installed globally.

Fix the `update()` and `select()` methods of the enum ticket model class.