Deactivate the DISTINCT in a SELECT on the right-hand side of an IN operator,
since it should not make any difference in the output but dues consume extra
memory and CPU time.
Fix a leaked statement handle in pager2.test.
Add a missing call to "test_sqlite3_log" to multiplex.test.
Optimizations to the OS sub-type checking in the Win32 VFS.
Omit a pointless OP_Null when processing a value-list RHS of an IN operator
where the LHS is a rowid.
Refactoring:  Change "pIndex->onError!=OE_None" to use a macro:
"IsUniqueIndex(pIndex)".  Easier to understand that way.
Enhance the PRAGMA integrity_check command to detect UNIQUE and NOT NULL
constraint violations.