Detect when a VdbeCursor is still pointing at a valid row but that row has
moved, and invalidated the return from prior sqlite3BtreeDataFetch() or
sqlite3BtreeKeyFetch() calls.
Add an ORDER BY test case to speedtest1.c
Add another performance test case to speedtest1.  This case is another
ORDER BY test but this time without LIMIT.
Adjust the repeat counts on several tests in speedtest1 so that the relative
time spent on the test is roughly the same regardless of --size.