Update cakin Groovy and Hydro how-to documentation for package.xml format 2

This merges the latest Indigo documentation, appropriately modified, into the branch used for Groovy and Hydro. Most of the changes are needed to support package.xml format 2, but there were some additional updates for errors found in the documentation review. 

previous discussions: #440 and #634

@dirk-thomas, @wjwwood, @tfoote: I doubt another full doc review is needed, but please look this over in case I missed something. Formatted copy is here: http://farnsworth.csres.utexas.edu/docs/catkin/groovy/html/

The only additional commit is 02a4248.