Bug 161174 Expect to set/get interval range with a 'String' param in GroupHandle.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/GroupHandle.java
* <li><code>INTERVAL_INTERVAL</code>
	 * 
	 * </ul>
	 * 
	 * @param interval
	 *            the interval value as a string
	 * @throws SemanticException
	 *             if the property is locked or the input value is not one of
	 *             the above.
	 */
	public void setInterval( String interval ) throws SemanticException
	{
		setStringProperty( GroupElement.INTERVAL_PROP, interval );
	}
	/**
	 * Returns the interval range of this group.
	 * 
	 * @return the interval range value as a double
	 */
	public double getIntervalRange( )
	{
		return this.getFloatProperty( GroupElement.INTERVAL_RANGE_PROP );
	}
	/**
	 * Returns the interval range of this group.
	 * 
	 * @param intervalRange
	 *            the interval range value as a double
	 * @throws SemanticException
	 *             if the property is locked.