Add a transaction so that these objects are cleared after the test run

Gets the specs to green and fixes issues #565 

Core problem was a missing transaction block around a spec in slugged_test.rb.  Once this spec ran, it left Manual objects with a slug of 'foo' in the database.   Those conflicted with Manual objects being created in the history_test.rb specs.

Intermittency of the failures was caused by ordering.  If the a spec in history_test.rb ran before the spec in slugged_test.rb it would pass, otherwise it would fail.