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
public synchronized static Map initViewerProps( ServletContext context,
			Map props )
	{
		
		if ( props == null )
			props = new HashMap( );
		
		String file = context.getInitParameter( INIT_PARAM_CONFIG_FILE );
		if ( file == null || file.trim( ).length( ) <= 0 )
			file = IBirtConstants.DEFAULT_VIEWER_CONFIG_FILE;
		try
		{
			InputStream is = null;
			if ( isRelativePath( file ) )
			{
				
				if ( !file.startsWith( "/" ) ) 
					file = "/" + file; 
				is = context.getResourceAsStream( file );
			}
			else
			{
				
				is = new FileInputStream( file );
			}
			
			PropertyResourceBundle bundle = new PropertyResourceBundle( is );
			if ( bundle != null )
			{
				Enumeration keys = bundle.getKeys( );