Improved PostgreSQL compatibility (support SHOW DEFAULT_TRANSACTION_ISOLATION).

h2/src/main/org/h2/command/Parser.java

@@ -801,6 +801,9 @@ public class Parser {
         if (readIf("CLIENT_ENCODING")) {
             // for PostgreSQL compatibility
             buff.append("'UNICODE' AS CLIENT_ENCODING FROM DUAL");
+        } else if (readIf("DEFAULT_TRANSACTION_ISOLATION")) {
+            // for PostgreSQL compatibility
+            buff.append("'read committed' AS DEFAULT_TRANSACTION_ISOLATION FROM DUAL");
         } else if (readIf("DATESTYLE")) {
             // for PostgreSQL compatibility
             buff.append("'ISO' AS DATESTYLE FROM DUAL");