PAGINATION_URL/PAGINATION_SAVE_AS implementation

allows the use of custom urls for pagination similar to *_URLS


haven't doc'd or written unit tests for it yet as i want to make sure it's a reasonable path to go down before putting in the effort. 

my use case is that all of my urls end in /, e.g. http://www.example.com/[category]/  and i'd like to have nice names on subsequent pages as well.   http://www.example.com/[category]/2/ rather than  http://www.example.com/[category]/index.2.html.