Add georss:box support and items agregation

I should have responded to this earlier, and I'm sorry about that, but there are a couple problems here:

• georss parsing has moved entirely into Format.GeoRSS -- all format parsing improvements should be made there. (This has a lot of benefits, although clearly in this case it causes pain.)
• Using the Boxes Layer is not recommended: instead, when possible a Vector layer should be created and used instead. The benefit of this is that it actually works and is not a dreadful hack -- the downside is that at the moment, tools for registering events on vector layers are slightly more clumsy, so if you are registering events on the boxes, this might need some further work.
• loadend events put into trunk in another patch/ticket
• popup width and height sound good to go into the georss layer as is, if the patch is reworked.

Not commenting on this earlier was my poor judgement, and I apologize for the delay. I'd like to help figure out how to get these things to happen in 2.6 if possible, so you have an upgrade path. If someone is still looking to work on this, please feel free to respond to any of these things which you have questions about, and we can work through them.

Mass ticket move to 2.7 post dev meeting. If you are actively working on this task, please update this ticket with information and change the milestone to 2.6. At the time of the next IRC meeting (most likely 1-31-08), this will mean the ticket can *not* be brought back into 2.6 unless there is further feedback.