[screenshot] Suggest to mix border effect and shadow effect

[Philippe Corbes <philippe corbes gmail com>]

Hello,

If we take a scennshot of a white window and we decide to add a shadow effect. the result woud better if we add a black square of one pixel.

I called this value "double" (= border + shadow). My new border effect is:
    --border-effect=border | shadow | double

What do you think about this? Would it be included in the trunc?

I'm ready to make a patch ;-)
Philippe Corbes