This experimental branch attempts to use columns for an index-on-expression

in place of the expression that is being indexed.  This particular check-in
mostly works, but there are still issues.

FossilOrigin-Name: 2e8d4fd4cfd9e82f33c707ba246fe2bb3ca01762cf5ac5905058fbc7adf0abe7

src/build.c

@@ -4192,6 +4192,7 @@ void sqlite3CreateIndex(
       j = XN_EXPR;
       pIndex->aiColumn[i] = XN_EXPR;
       pIndex->uniqNotNull = 0;
+      pIndex->bHasExpr = 1;
     }else{
       j = pCExpr->iColumn;
       assert( j<=0x7fff );