Markdown.Sanitizer removes <a href= and <img src= tags referencing relative paths

[GoogleCodeExporter]

The part 
    (https?:\/\/|\/)
in Markdown.Sanitizer var img_white only allows full URLs:
    http://... or https://...
or in-site URLs relative to the root
    /...

As a consequence, the markdown code 
      ![buttons](js/pagedown/wmd-buttons.png)"

producing the html code

    <img src="js/pagedown/wmd-buttons.png" alt="buttons" title="" />

is removed by Markdown.Sanitizer, because the in-site URL is relative to the 
current path. 

The same applies to var a_white

Solution:
Add an extra ? as follows:
    (https?:\/\/|\/?)

Original issue reported on code.google.com by [email protected] on 9 Oct 2014 at 12:44