unnecessary exception patch

Hi,

this is a patch that avoids getting an undeserved PSQLException when setting
the transaction isolation level on a connection:

---
postgresql-jdbc-8.2-507.src/org/postgresql/jdbc2/AbstractJdbc2Connection.java
2007-12-01 11:17:49.000000000 +0200
+++ src/org/postgresql/jdbc2/AbstractJdbc2Connection.java       2008-01-11
15:26:58.000000000 +0200
@@ -759,6 +759,8 @@
      */
     public void setTransactionIsolation(int level) throws SQLException
     {
+       if (level == getTransactionIsolation())
+               return;
         if (protoConnection.getTransactionState() !=
ProtocolConnection.TRANSACTION_IDLE)
             throw new PSQLException(GT.tr("Cannot change transaction
isolation level in the middle of a transaction."),
                                     PSQLState.ACTIVE_SQL_TRANSACTION);


It applies to the case when a connection is reused within a connection pool
and some of its properties are automatically reset before the connection is
handed to the requesting party.
Example: the default DriverManagerConnectionProvider in Hibernate.

Regards.