Check if image responds to :read

[duhast]

Hi! This update allows to source image from "alternate" file implementations like CarrierWave::Storage::Fog::File and CarrierWave::SanitizedFile.

Very convenient when you're working with images stored remotely.

[petergoldstein]

@duhast I know it's been a very long time, but do you still have interest in this PR? If so, any chance you can rebase and add a spec for the "alternate" file implementation case?

[duhast]

Oh yeah, it's been a long time 😄

I have this patch working in production for couple years already, however I don't think I'll have time to work on the spec for PR in near future.

[petergoldstein]

@duhast Ok, thanks. I'd like to see this merged, and a spec would help get it there. If you have any suggestions for how to build a spec, they'd be appreciated.