Expose 'catalogue' method as consistent API in example groups

In rspec-puppet pre-1.0, the catalogue method was available in all example
groups with no arguments.  This has been restored, so the catalogue is easily
accessible in derivative example groups where subject is overridden (e.g.
so subject can be redefined as a resource inside the catalogue).
Merge pull request #145 from domcleal/catalogue-method

Expose 'catalogue' method as consistent API in example groups