Modify the query planner interface so that it always passes in the result set.

This is the first step toward adding an optimization that will omit tables
from a join that do not contribute to the result.

FossilOrigin-Name: 2c2577e69ccb47f1af674a755e71221e2ca0b322

src/sqliteInt.h

@@ -1974,6 +1974,7 @@ struct SrcList {
 #define WHERE_AND_ONLY         0x0080 /* Don't use indices for OR terms */
 #define WHERE_GROUPBY          0x0100 /* pOrderBy is really a GROUP BY */
 #define WHERE_DISTINCTBY       0x0200 /* pOrderby is really a DISTINCT clause */
+#define WHERE_WANT_DISTINCT    0x0400 /* All output needs to be distinct */
 
 /* Allowed return values from sqlite3WhereIsDistinct()
 */