When replacing a post with the same file, don't queue a deletion and
don't leave a comment or modaction. There's no need to do these things
when we're restoring a missing or corrupted image with the original file.
* Adds a "Tags" field to the post replacement dialog box. The given tags
are added to the post after replacement.
* Prefills the Tags field with certain tags that usually need to be
removed after replacement: replaceme, image_sample, jpeg_artifacts, etc.
* Record "file://#{filename}" as the replacement url when the
replacement comes from an uploaded file.
* Record the actual url downloaded by the upload process otherwise. This
may be different from the url given by the user, since the upload
process may rewrite the url.
Adds a "Final Source" field to the post replacement dialog. If
specified, the post's source field will be changed to this value after
replacement.
This makes fixing the source back to the HTML page after
replacement easier.
