Change the name of the Index.autoIndex field to Index.idxType and provide

symbolic names for the various values of that field rather than using
magic numbers.

FossilOrigin-Name: d16e575dacc811de0f7b58a0d1cd243678dce6c5

src/fkey.c

@@ -233,8 +233,8 @@ int sqlite3FkLocateIndex(
       if( zKey==0 ){
         /* If zKey is NULL, then this foreign key is implicitly mapped to 
         ** the PRIMARY KEY of table pParent. The PRIMARY KEY index may be 
-        ** identified by the test (Index.autoIndex==2).  */
-        if( pIdx->autoIndex==2 ){
+        ** identified by the test.  */
+        if( IsPrimaryKeyIndex(pIdx) ){
           if( aiCol ){
             int i;
             for(i=0; i<nCol; i++) aiCol[i] = pFKey->aCol[i].iFrom;