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
.getInitParameter( INIT_PARAM_BIRT_RESOURCE_PATH ), null, false );
		
		String s_overwrite = DataUtil.trimString( context
				.getInitParameter( INIT_PARAM_OVERWRITE_DOCUMENT ) );
		if ( "true".equalsIgnoreCase( s_overwrite ) ) 
		{
			isOverWrite = true;
		}
		else
		{
			isOverWrite = false;
		}
		
		initProps = initViewerProps( context, initProps );
		
		String flag = DataUtil.trimString( context
				.getInitParameter( INIT_PARAM_PRINT_SERVERSIDE ) );
		if ( IBirtConstants.VAR_ON.equalsIgnoreCase( flag ) )
		{
			isSupportedPrintOnServer = true;
		}
		else if ( IBirtConstants.VAR_OFF.equalsIgnoreCase( flag ) )
		{
			isSupportedPrintOnServer = false;
		}
		
		clearTempFiles( );
		
		isInitContext = true;
	}