Backport the RTree implementation from the trunk into the 3.6.23 branch.
The code for the application-defined query boxes is still present but
is disabled.  The reason for this backport is to take advantage of recent
enhancements to robustness to database corruption.

FossilOrigin-Name: 854b23c117c973fcf63f31bda189b7492595c3f9
4 files changed