Fix #542

Page link may contain duplicate starting forward slashes.
//page points to http://page/ when what we want is
/page pointing to http://localhost:1234/page

lib/gollum/markup.rb

@@ -407,6 +407,12 @@ module Gollum
           presence  = "present"
         end
         link = ::File.join(@wiki.base_path, page ? page.escaped_url_path : CGI.escape(link_name))
+
+        # //page is invalid
+        # strip all duplicate forward slashes using helpers.rb clean_url
+        # //page => /page
+        link = clean_url link
+
         %{<a class="internal #{presence}" href="#{link}#{extra}">#{name}</a>}
       end
     end