Add --blind-copy mode

[RhetTbull]

I can see how this would hurt performance especially when connecting to a NAS. If you made the assumption that OSXPhotos was the only writer to the export directory and no modifications were being made to files by the user you could you rely entirely on the exportedb without checking the photo files to see if it has changed?

Yes, if you assumed no other process/person was writing to the directory and that you started with an empty directory, this could be optimized. Today, OSXPhotos lists the contents of the export directory to see if there's a possible name collision when writing a new file. You would still need to check for name collisions but the code could do this by querying the export database to see if a photo with that name was already exported and this would be faster than a directory read over a NAS. I'll open an issue to add an option for this but not sure when I'll get to it.

Originally posted by @RhetTbull in #1722 (reply in thread)