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
break;
				case '"' :
					sbHtmlEncoded.append( "&#34;" ); 
					break;
				case '\'' :
					sbHtmlEncoded.append( "&#39;" ); 
					break;
				case '<' :
					sbHtmlEncoded.append( "&#60;" ); 
					break;
				case '>' :
					sbHtmlEncoded.append( "&#62;" ); 
					break;
				case '`' :
					sbHtmlEncoded.append( "&#96;" ); 
					break;
				case '&' :
					sbHtmlEncoded.append( "&#38;" ); 
					break;
				default :
					sbHtmlEncoded.append( c );
			}
		}
		sHtmlEncoded = sbHtmlEncoded.toString( );
		return sHtmlEncoded;
	}
	/**
	 * This function is used to decode a htmlEncoded string and convert to the
	 * orginial string
	 *