Add a hook to alter the image URL before downloading

I have encountered a somewhat unusual use case. The image tags on the ASP.NET-based blog I'm importing from look like <img src="something.ashx"> where .ashx is an extension used in ASP.NET to do some server-side processing of the image. The actual output sent to the browser is in .jpg format.

Since .ashx is not in the list of valid extensions in FIG, FIG rejects the image and the Feeds Importer tells me the post failed to import.

In my case, the same images are available on the origin server if I simply change the extension from .ashx to .jpg. So, I needed a way to alter the URL before FIG downloads the file. Since FIG doesn't expose any hooks, I had to write my own. See the attached patch.

I'm not sure if this is going to be useful for anyone else, but I'm documenting it here just for the record.