patch for image.el

[chrisl]

Hi,

I'm using GNU emacs 21.3.1 under Linux.  I discovered that image.el
didn't recognize some of my jpeg files (it reported them as not being
image files).  By using file(1) and looking at the magic(5) file, I
saw that there is a different jpeg format in addition to JFIF: Exif.
I also found that image-jpeg-p can cause substring to run past the end
of the data array, which causes an error.  I made the following change
that fixes both problems:

67,69c67
<                    (string-match "JFIF\\|Exif" 
<                                  (substring data i 
<                                             (min (+ i nbytes) len)))))
---
>                    (string-match "JFIF" (substring data i (+ i nbytes)))))

Thanks for maintaining The One True Editor. :)

- Chris