acts_as_journalized changed the interfaces and didn't include all of
the recent changes to the Journals system.

* removed Journal diffs, acts_as_journalized handles them differently
* fixed the Journal atom feed
* added the journal preview back in
* added missing tests

http://www.flickr.com/photos/thebrownhouse/4599233853/sizes/l/

Database detection library. #112

This module can be used to gather information about the currently used
database.

Fix test errors on 1.8.6 after acts_as_journalized merge. #413

Fix test errors on 1.9.2 after acts_as_journalized merge. #412

Remove returning since it causes deprecation warnings. #414

Conflicts:
	test/unit/journal_test.rb
	vendor/plugins/acts_as_journalized/lib/redmine/acts/journalized/permissions.rb