More flexible response reporting in wp-plupload.js

[ippetkov]

The wp-plupload.js wrapper to the plupload library only returns server responses to bound callbacks in the case of a well formed error (the server responds with { success: false } ).

Sometimes it may be useful to receive additional information from the server on successful upload. I have prepared a patch that allows for the success and error callbacks to receive server responses.

[wonderboymusic]

In 34009:

WP Plupload: on FileUploaded, allow success and error callbacks to receive server responses after a successful upload.

Props ippetkov.
Fixes #24934.

[wonderboymusic]

In 34047:

Revert [34009], broke uploads.

See #24934.

[wonderboymusic]

On a successful upload, false-positive errors are propagating to the front end. Uploads that were successful aren't appearing until a full-page refresh.

[kitchin]

The problem was the early return after else {, not the self.success data at the end.