Enhancements to PRAGMA optimize and ANALYZE. Add the 0x10000 flag to

Enhancements to PRAGMA optimize and ANALYZE.  Add the 0x10000 flag to
PRAGMA optimize.  ANALYZE now records zero-size partial indexes in the
sqlite_stat1 table.  PRAGMA optimize looks for both growth and shrinkage
in table sizes, and uses tighter bounds (10x rather than 25x) to trigger
a re-analyze.  PRAGMA optimize automatically uses are reasonable
analysis_limit to prevent excessive runtimes.

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