Relative links don't work in the demo, parenthesis => %2a

```
What steps will reproduce the problem?
1. Go to demo http://pagedown.googlecode.com/hg/demo/browser/demo.html
2. Add this text to the unsanitized text box:
"See my [About](about/) page for details."
Example like: http://daringfireball.net/projects/markdown/syntax#link

What is the expected output? What do you see instead?
Expected the link to be to "about/", but it was to
http://pagedown.googlecode.com/hg/demo/browser/%2aabout%2a/
Is my markdown syntax right?

What version of the product are you using? On what operating system?

Current live web demo on current Chrome OSX.

Please provide any additional information below.

```

Original issue reported on code.google.com by `Jamshi...@gmail.com` on 22 Dec 2012 at 9:09