fix markdown class for new php

lib/markdown.php

@@ -239,7 +239,7 @@ class Markdown_Parser {
   var $predef_titles = array();
 
 
-  function Markdown_Parser() {
+  function __construct() {
   #
   # Constructor function. Initialize appropriate member variables.
   #
@@ -1692,7 +1692,7 @@ class MarkdownExtra_Parser extends Markdown_Parser {
   var $predef_abbr = array();
 
 
-  function MarkdownExtra_Parser() {
+  function __construct() {
   #
   # Constructor function. Initialize the parser object.
   #