markdown: some lines are lost in verbatim blocks inside a list

[xymus]

The markdown module loses some lines from verbatim blocks inside list items. As far as I can tell, it happens only when the number of non-whitespace characters in the line is equal to the indentation level.

For example, if the indentation uses 4 spaces, 4 letter lines are cut:

*   4 spaces, `asdf` and `tab.` are lost
    ~~~
    a
    as
    asd
    asdf
	tab.
    asdfg
    ~~~

And the nitmd output, notice the blank lines:

<ul>
<li><p>4 spaces, <code>asdf</code> and <code>tab.</code> are lost</p>
<pre><code>a
as
asd


asdfg
</code></pre>
</li>
</ul>

The same thing happens with a 2 spaces indentation:

* 2 spaces, `as` is lost

  ~~~
  a
  as
  asd
  asdf
  ~~~

And the nitmd output:

<ul>
<li><p>2 spaces, <code>as</code> is lost</p>
<pre><code>a

asd
asdf
</code></pre>
</li>
</ul>

I get this behavior with nitmd and when using the markdown module directly.