Allow objects with future dates to display in date based generic views

[scaba]

The date based generic views are coded to only show objects whose given date field is <= now. However, for views of something like an events calendar, one needs to display objects whose date field is >= now. Proposed is to add an "upcoming_index", which sorts ascending, for showing future objects, and a "future_ok=False" keyword argument to the "archive_(year, month,day)" and "object_detail" views.

[scaba]

For doc updates:

New view:

upcoming_index

• A top-level index page showing the "next upcoming" objects. Has an optional argument, num_upcoming, which is the number of items to display on the page (defaults to 15).

• Uses the template app_label/module_name_upcoming by default.

• Has the following template context:

date_list

List of years with objects

upcoming

Upcoming objects by date

Updated views:

archive_year, archive_month, archive_day and object_detail all accept an optional keyword argument future_ok which defaults to False, which is the current behavior of these views.

[James Bennett]

Superseded by #2433, which has a more up-to-date patch.