Fix high disk space usage for local files

[Stanislas Chevallier]

Hi,

I found out an app I'm developing was using 2.5G of disk space for its image cache even though every loaded images are from disk and I manage thumbnails myself, so literally no files should be in the SDWebImageCache folder.

It appears there is no detection of local files when downloading them with SDWebImageCache so I added a quick setting to prevent local images to be stored on disk.

Here is a preview of the commit in my fork dealing with this :

3543b75

Thanks for considering,

Stan

[Alex Türk]

Awesome solution. I had the same problem :)