Update comments in the R-Tree module in preparation for some big changes.
Add an "rtree" performance test to speedtest1.
Add the --verify option to speedtest1.  Add verification test cases to
the "rtree" testset and a case that uses a custom geometry callback.
Add the new interfaces to rtree, though they do not yet work.  Add the
"show_speedtest1_rtree.tcl" script for showing the test data used for the
R-Tree tests of speedtest1.  Change speedtest1 to generate better R-Tree
test data.
Continuing clean-up of the R-Tree module in preparation for cutting in the
new generalized query mechanism.
Continuing work on the new custom query mechanism for r-tree.
Remove over 300 lines of unused code, code that implemented the older 
Guttman insertion algorithms that are no longer used.
Fix comments on the rtreenode() and rtreedepth() test function in the R-Tree
module.
Initial attempt at getting R-Tree queries to work using a priority queue.
This check-in compiles, but R-Trees do not work well.  And there are
debugging printf()s left in the code.  This is an incremental check-in.
Bug fixes to the priority-queue implementation for R-Trees.  Improved tracing
capability.  Some queries work now, but still many problems.
Fix a bug in rowid=? query handling.  More problems remain.
TCL tests now all pass.
Convert the RTree module query mechanism over to using a priority queue for
walking the RTree.
Performance optimization on nodeGetCell() in R-Tree.
Refactor the constraint checking logic in RTree.  The new-style constraint
callbacks created by sqlite3_rtree_query_callback() are now hooked up from
end to end, though still untested.
Test cases and bug fixes for the sqlite3_rtree_query_callback()
mechanism.
More test cases with very long priority queues.
Performance optimization on byte-swapping in R-Tree.
Merge the latest changes from sessions.
Further improvements to the RTREE_DECODE_COORD() method, to take advantage
of known processor byte orders when available.  This makes the code 3% faster,
according to valgrind.  Also add test cases to make sure the on-disk
representation is correct.
Clean up the proper-subset cost adjustment logic to make it more compact
and easier to read and so that full branch test coverage is more easily
obtained.