Remove unreachable code, replacing it in most cases with assert() or NEVER()
macros.
Add a way for virtual tables to return the expected number of rows for a scan (not just the overall cost) to SQLite. Have the rtree module make use of this.
Fix typos in compile and run-time tests of the sqlite library version number in  rtree.c.
Add a comment to the sqlite3_index_info structure indicating that the new
field is only available in SQLite 3.8.2 or later.
Fix an error message in the spellfix extension so that it conforms to the 
style of error messages in the core.