Bug 183919 [Enhancement] add a switch to determine whether to clean viewer image folder when session expires
in current viewer implementation, file in image folder is deleted when its corresponding session expires, could viewer add a switch to allow users to decide whether this deletion operation should be performed.
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/utility/ParameterAccessor.java
{
		String defaultName = "BIRTReport"; 
		String fileName = defaultName;
		BaseAttributeBean attrBean = (BaseAttributeBean) request
				.getAttribute( IBirtConstants.ATTRIBUTE_BEAN );
		if ( attrBean == null )
			return fileName;
		String baseName = attrBean.getReportDesignName( );
		if ( baseName == null || baseName.length( ) == 0 )
			baseName = attrBean.getReportDocumentName( );
		if ( baseName == null || baseName.trim( ).length( ) <= 0 )
			return fileName;
		int index = baseName.lastIndexOf( '/' );
		if ( index == -1 )
			index = baseName.lastIndexOf( '\\' );
		
		
		if ( index != -1 )
		{
			baseName = baseName.substring( index + 1 );
		}
		
		
		
		int dotIndex = baseName.lastIndexOf( '.' );
		if ( dotIndex > 0 )
		{
			fileName = baseName.substring( 0, dotIndex );
		}