Fix deprecation warnings on Rails 3.2

* Fixed the `set_table_name` deprecation warnings on 3.2, bumping the Rails gem requirements to 3.0.9 onwards as required.
* Modified Rakefile to load the engine, allowing `rake db:create` and `rake db:migrate` to be run before spec, which allows the currently broken tests to run successfully.
* Added travis support, testing against the latest Rails 3.0, 3.1 and 3.2 revisions.
* Removed the debugger require from the spec so that this will run happily with Ruby 1.9.3.