…ner and Takeshi Komiya:

- Added the class variable 'builder' to Catalog class, so any instances of Catalog can access the information within the builder, including things such as app, config, srcdir, outdir etc.. see MessageCatalogBuilder for details.
- Initialise this Catalog.builder as the instance of MessageCatalogBuilder is created, ie. in the init()
- As Message class is created, list of locations passing to it will be made singular, using set(), sorted alphabetically for easier searching and identifying origins where the message can be found.
- source dir is used within the __iter__ of the Catalog, using sphinx.util.osutil.relpath, for safer functionality, to work out the relative path for each location entry.