[Xastir] rtree speeds up shapefiles

[Jason Winningham]

For all you TIGERmap uses who can't get a map today, maybe you're ready 
for some shapefiles. (:

I just turned on rtree support and it made a huge difference in the 
redraw of my maps.  I'm using several shapefiles from National Atlas 
and NOAA that cover the entire country, but I generally only view a 
small area (zoom level 128 to 512 is where I typically view).

The first time these maps are drawn it takes the usual amount of time, 
but the redraws are really fast on my G5.  Zoom in, zoom out, pan, 
doesn't matter.

If xastir has to render all of a large shape file it isn't going to 
help, but if you usually view a small part of a large shapefile it's 
worth adding --with-rtree to your ./configure command.

Whoever came up with the idea and the code for the rtree stuff, thanks.

-Jason
kg4wsv