Set the TF_StatsUsed flag on tables when the query planner outcome is

affected by the sqlite_stat1 data.  Also, change the column names of the
"PRAGMA stats" command so that they are not keywords.

FossilOrigin-Name: fb2b8ae8310e4ea4b42354bbf36c3084a9d5c6d7

src/whereInt.h

@@ -395,8 +395,13 @@ struct WhereLoopBuilder {
   UnpackedRecord *pRec;     /* Probe for stat4 (if required) */
   int nRecValid;            /* Number of valid fields currently in pRec */
 #endif
+  unsigned int bldFlags;    /* SQLITE_BLDF_* flags */
 };
 
+/* Allowed values for WhereLoopBuider.bldFlags */
+#define SQLITE_BLDF_INDEXED  0x0001   /* An index is used */
+#define SQLITE_BLDF_UNIQUE   0x0002   /* All keys of a UNIQUE index used */
+
 /*
 ** The WHERE clause processing routine has two halves.  The
 ** first part does the start of the WHERE loop and the second