Custom header image cropping can create identical attachments

[SergeyBiryukov]

1. Add an image to Media Library which requires cropping.
2. Go to Appearance → Header, click "Choose from image library".
3. Select the image from point 1, click "Set as header", "Crop and Publish".
4. Press browser's Back button, click "Crop and Publish" once again.
5. Delete one of the two identical "Header Image" attachments in Media Library.
6. The other attachment is now orphaned (the files are deleted in point 5).

Sounds like wp_unique_filename() should be used in there somewhere.

Related: #19840, #20657

Perhaps we should also call wp_upload_dir() to get a newly dated upload dir instead of reusing the old dir when cropping an existing image from the media library.

20666.2.patch​ fixes the line placement (should be after wp_mkdir_p()).

Replying to ryan:

Perhaps we should also call wp_upload_dir() to get a newly dated upload dir instead of reusing the old dir when cropping an existing image from the media library.

step_3() in wp-admin/custom-header.php would still expect the new attachment to be in the same directory as the original file:
​http://core.trac.wordpress.org/browser/trunk/wp-admin/custom-header.php?rev=20769#L877

In [20787]:

Make the file names unique for cropped header images. Props SergeyBiryukov. fixes #20666