CMYK jpeg images were being read as 4 channel images, even though they

CMYK jpeg images were being read as 4 channel images, even though they
have no alpha channel.

The colors were being transferred directly from the JPEG image data,
this only looked correct because of an old bug in photoshop, kept for
compatibility in later versions.  Photoshop inverts the ink values in
the file, so max cyan coverage is stored at 0, and min as 255, and so
on.

CMYK jpegs are now read as 3 channel images.  The colors are now
converted adjusting for the photoshop bug, cmyk images from the only
other source I have, corel draw 9, are inverted in the same way,
presumably for compatibility with photoshop.

If anyone has an application that produces technically correct CMYK
jpegs, please provide a sample in jpeg and tiff form so I can attempt
to deal with it.

Fixes: http://rt.cpan.org/Ticket/Display.html?id=20416