Cleanup (minor): removed some references to experimental versions.
Placed the R-tree (spatial index) code right into the source tree instead of treating it as a library. Two reasons for doing this: 1) avoid confusion: the public domain R-tree code by Guttman can be found on the internet, but we are using a version that was rearranged by people at Guelph to produce a smaller header file and hide implementation details as much as possible; 2) allow us to tweak the library for speed improvements.