Detect dupes on copy/move

[Marsu42]

On copy/move, XnViewMP doesn't detect at all if the image already in place is an exact duplicate and let's the user compare even if it would take a computer a few nanoseconds to to that.

This is annoying when it occurs often like when having downloaded a bulk of images from the web with a bot and then trying to sort the desired ones into an existing directory. Just now, it's more effective to just copy/move into a new directory, and then let a dedicated dupe searcher do the elimination step.

Suggestion: Add an option "don't copy/move on exact duplicate" to skip the comparison dialog in these cases.