perf: execute "SET application_name" if name has changed only

This improves cases when application is setting the same name again and again (e.g. glassfish3).

See http://www.postgresql.org/message-id/flat/CADK3HHJKRq09otwqtv3rtnDh9h_LqFvBz+BHKgHjZgtnybvF1g@mail.gmail.com

closes #537

pgjdbc/src/main/java/org/postgresql/core/ProtocolConnection.java

@@ -186,4 +186,10 @@
   * @return backend timezone in java format.
   */
  TimeZone getTimeZone();

  /**
   * Returns application_name connection property.
   * @return application_name connection property
   */
  String getApplicationName();
}

pgjdbc/src/main/java/org/postgresql/core/v2/ProtocolConnectionImpl.java

@@ -234,6 +234,11 @@ public TimeZone getTimeZone() {
    return TimeZone.getDefault();
  }

  @Override
  public String getApplicationName() {
    return "";
  }

  private String serverVersion;
  private int serverVersionNum = 0;
  private int cancelPid;

pgjdbc/src/main/java/org/postgresql/core/v3/ProtocolConnectionImpl.java

@@ -245,6 +245,18 @@ public TimeZone getTimeZone() {
    return timeZone;
  }

  void setApplicationName(String applicationName) {
    this.applicationName = applicationName;
  }

  @Override
  public String getApplicationName() {
    if (applicationName == null) {
      return "";
    }
    return applicationName;
  }

  /**
   * True if server uses integers for date and time fields. False if server uses double.
   */
@@ -279,4 +291,9 @@ public TimeZone getTimeZone() {
   * TimeZone of the current connection (TimeZone backend parameter)
   */
  private TimeZone timeZone;

  /**
   * application_name connection property
   */
  private String applicationName;
}

pgjdbc/src/main/java/org/postgresql/core/v3/QueryExecutorImpl.java

@@ -2091,6 +2091,9 @@ protected void processResults(ResultHandler handler, int flags) throws IOExcepti
          if ("TimeZone".equals(name)) {
            protoConnection.setTimeZone(TimestampUtils.parseBackendTimeZone(value));
          }
          if ("application_name".equals(name)) {
            protoConnection.setApplicationName(value);
          }
          break;
        }

pgjdbc/src/main/java/org/postgresql/jdbc/PgConnection.java

@@ -1385,6 +1385,10 @@ public void setClientInfo(String name, String value) throws SQLClientInfoExcepti
      if (value == null) {
        value = "";
      }
      final String oldValue = protoConnection.getApplicationName();
      if (value.equals(oldValue)) {
        return;
      }

      try {
        StringBuilder sql = new StringBuilder("SET application_name = '");
@@ -1435,11 +1439,13 @@ public void setClientInfo(Properties properties) throws SQLClientInfoException {

  public String getClientInfo(String name) throws SQLException {
    checkClosed();
    _clientInfo.put("ApplicationName", protoConnection.getApplicationName());
    return _clientInfo.getProperty(name);
  }

  public Properties getClientInfo() throws SQLException {
    checkClosed();
    _clientInfo.put("ApplicationName", protoConnection.getApplicationName());
    return _clientInfo;
  }

pgjdbc/src/test/java/org/postgresql/test/jdbc4/ClientInfoTest.java

@@ -56,6 +56,22 @@ public void testSetAppName() throws SQLException {
    assertEquals("my app", _conn.getClientInfo().getProperty("ApplicationName"));
  }

  public void testExplicitSetAppNameNotificationIsParsed() throws SQLException {
    if (!TestUtil.haveMinimumServerVersion(_conn, "9.0")) {
      return;
    }

    String appName = "test-42";

    Statement s = _conn.createStatement();
    s.execute("set application_name='" + appName + "'");
    s.close();
    assertEquals("application_name was set to " + appName + ", and it should be visible via "
        + "con.getClientInfo", appName, _conn.getClientInfo("ApplicationName"));
    assertEquals("application_name was set to " + appName + ", and it should be visible via "
        + "con.getClientInfo", appName, _conn.getClientInfo().get("ApplicationName"));
  }

  public void testSetAppNameProps() throws SQLException {
    if (!TestUtil.haveMinimumServerVersion(_conn, "9.0")) {
      return;