Add required psqldir setting for isolation checks.

src/tools/msvc/vcregress.pl

@@ -144,7 +144,9 @@ sub isolationcheck
 	copy("../../../$Config/isolation_tester/isolation_tester.exe",".");
     my @args = (
 				"../../../$Config/pg_isolation_regress/pg_isolation_regress",
-			"--inputdir=.",  "--schedule=./isolation_schedule"
+				"--psqldir=../../../$Config/psql",
+				"--inputdir=.",  
+				"--schedule=./isolation_schedule"
 			   );
     push(@args,$maxconn) if $maxconn;
     system(@args);