Experimental change to support the covering index optimization for queries with OR terms in the WHERE clause that search a single index more than once.

FossilOrigin-Name: 1dc8c7c741a82bb98a07f3fdb8142d8bc8d8a98b

src/sqliteInt.h

@@ -1948,6 +1948,7 @@ struct WhereLevel {
       } *aInLoop;           /* Information about each nested IN operator */
     } in;                 /* Used when plan.wsFlags&WHERE_IN_ABLE */
   } u;
+  Index *pCovidx;       /* Possible covering index for WHERE_MULTI_OR levels */
 
   /* The following field is really not part of the current level.  But
   ** we need a place to cache virtual table index information for each