Bug 176681 Issue about creating context-parameter path in read-only path[0601]
Description: Issue about creating context-parameter path in read-only path Build number:2.2.0.v20070308 Steps to reproduce: 1. Deploy birt. 2. Set BIRT_VIEWER_DOCUMENT_FOLDER/BIRT_VIEWER_IMAGE_DIR/.. to a read-only path. 3. Preview report. Expected result: Because the path is read-only, folders should be created in ${java.io.tmpdir} Actual result: No folders are created in ${java.io.tmpdir} and reports cannot be previewed in frameset mode.
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/utility/ParameterAccessor.java
*            default parameter value
	 * @return new query string with new parameter value
	 */
	public static String getEncodedQueryString( HttpServletRequest request,
			String name, String value )
	{
		String queryString = ""; 
		Enumeration e = request.getParameterNames( );
		Set nullParams = getParameterValues( request, PARAM_ISNULL );
		boolean isFirst = true;
		while ( e.hasMoreElements( ) )
		{
			String paramName = (String) e.nextElement( );
			if ( paramName != null
					&& !paramName.equalsIgnoreCase( PARAM_ISNULL ) )
			{
				String paramValue = getParameter( request, paramName, false );
				if ( nullParams != null
						&& nullParams.remove( toUTFString( paramName ) )
						&& !paramName.equalsIgnoreCase( name ) ) 
				
				
				{
					paramName = urlEncode( paramName, ISO_8859_1_ENCODE );
					queryString += ( isFirst ? "" : PARAMETER_SEPARATOR ) + PARAM_ISNULL + EQUALS_OPERATOR + paramName; 
					isFirst = false;
					continue;
				}
				if ( paramName.equalsIgnoreCase( name ) )
				{