[Radiant] Alias Page Extension

[Daniel Sheppard]

> Are you sure that's what subclasses_of does? I know that 
> there's definitely a method on ActiveRecord::Base that keeps track of
> subclasses as their created - maybe it's called something 
> else - descendants maybe? - I can't remember, but I'm pretty sure it
> exists.

lounge groggy # ruby script/console
Loading development environment.
>> Page.descendants
=> [AtomPage, AlphabetIndexPage, AlphabetPage, GroggyFileNotFoundPage, GroggyRootPage, GroggyFestivalPage, GroggyArticlePage,
GigParentPage, ArchivePage, EnvDumpPage, ArchiveDayIndexPage, ArchiveMonthIndexPage, FileNotFoundPage, ArchiveYearIndexPage,
VenuePage]
>> FileNotFoundPage.descendants
=> [GroggyFileNotFoundPage]