Bug 153412 Change parameter type will cause preview fail
Description: Change parameter type will cause preview fail Steps to reproduce: 1. New a report paramter, string, text-box, default value is abc. 2. Drag the parameter to Layout and preview. 3. Change the parameter's type to integer, list-box, add a value 1 4. Preview Expected result: No errors. Actual result: The value "abc" is invalid with the type "integer".
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/context/ViewerAttributeBean.java
* Report parameters as string map
	 */
	private Map parametersAsString = null;
	/**
	 * Report parameter definitions List
	 */
	private Collection parameterDefList = null;
	/**
	 * Display Text of Select Parameters
	 */
	private Map displayTexts = null;
	/**
	 * Constructor.
	 * 
	 * @param request
	 */
	public ViewerAttributeBean( HttpServletRequest request )
	{
		try
		{
			init( request );
		}
		catch ( Exception e )
		{
			this.exception = e;
		}
	}
	/**
	 * Init the bean.
	 *