Needs file:// prefix when inserting an image

[arctrong]

Issue description

Needs file:// prefix when inserting an image.

Markdown to reproduce

The following doesn't work:

![](pict/myimage.png)

The following works:

![](file://pict/myimage.png)

Impact

Python-markdown module produces the following:

<img alt="" src="file://pict/myimage.png" />

that's not correct. I want it to reference the local file location:

<img alt="" src="pict/myimage.png" />