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
if ( canWrite && new File( realPath ).canWrite( ) )
					return realPath;
			}
			catch ( Exception e )
			{
			}
		}
		
		if ( isRelative )
		{
			realPath = DataUtil.trimSepEnd( System
					.getProperty( "java.io.tmpdir" ) ) + path; 
		}
		else
		{
			
			if ( defaultPath != null )
				realPath = DataUtil.trimSepEnd( System
						.getProperty( "java.io.tmpdir" ) ) + File.separator + defaultPath; 
		}
		
		makeDir( realPath );
		return realPath;
	}
	/**
	 * Returns real path relative to context
	 * 
	 * @param path
	 * @param context
	 * @return