[Radiant] Extension load order

[Daniel Sheppard]

> Rails has just changed their mechanism for plugin loading:
> 
> http://ryandaigle.com/articles/2007/9/24/what-s-new-in-edge-rails-specify-plugin-load-order
> 
> Basically, you specify the load order of plugins that you care about and then just add the
> :all symbol to substitute in all the remaining plugins.

This is now in core. Should make the use of Shards more comfortable.

Dan.