Reduce the amount of code used to implement OP_SeekGe and similar.
Changing the CAST behavior of REAL values actually changed a documented
requirement.  So we also have to change the requirement evidence text to
match.
Add requirements test cases for determining when an expression is true and
when it is false.
Make sure the update hook is not invoked for WITHOUT ROWID tables, as
the documentation specifies.  This bug was found while adding requirements
marks, so a few extraneous requirements marks are included in this
check-in.
Add additional test cases and requirements evidence marks for WITHOUT ROWID.
Add additional test cases for skip-scan.
Avoid using the GetVersionEx functions if they are considered deprecated.
Avoid using the GetVersionEx functions if they are considered deprecated.
Lower the threshold for using skip-scan from 50 to 18, based on experiments
that show that 18 is the approximate break-even point for a variety of
schemas.
Make sure the colWidth array is correctly initialized in the ".explain"
command of the shell.
Additional test cases for skip-scan.
Fix some harmless compiler warnings in speedtest1.exe.
Fix spelling typo in speedtest1.exe.
Update documentation of sqlite3_column() for clarity.  Update evidence marks
on test cases.
Remove unnecessary local variables from sqlite3VdbeExec() in order to
reduce stack-space requirements of that routine.
Merge all recent trunk changes.