image/jpeg: support progressive mode images

[bradfitz]

This is a feature request bug for progressive image support in image/jpeg.

image/jpeg's reader.go contains:

                case marker == sof2Marker: // Start Of Frame (Progressive).                                                           
                        err = UnsupportedError("progressive mode")

Facebook (or some version of the Facebook mobile app maybe?) seems to encode JPEGs as
progressive when scaling them down, which means I can't read them.

Attached is an example.

Attachments:

1. 255256_10151183168140090_1533251541_n.jpg (90710 bytes)

[robpike]

Comment 1:

Owner changed to @nigeltao.

Status changed to Accepted.

[rsc]

Comment 2:

Labels changed: added go1.1maybe.

[nigeltao]

Comment 3:

This issue was closed by revision 8b624f6.

Status changed to Fixed.

[bradfitz]

Comment 4:

Thanks, Nigel! :)