image/jpeg: send a correct Start Of Scan (SOS) header.
image/jpeg: send a correct Start Of Scan (SOS) header.

Section B.2.3 of http://www.w3.org/Graphics/JPEG/itu-t81.pdf discusses
the End of spectral selection (Se) byte.

Apparently many JPEG decoders ignore the Se byte (or let it through
with a warning), but some configurations reject them. For example,
http://download.blender.org/source/chest/blender_2.03_tree/jpeg/jcmaster.c
has these lines:

if (Ss != 0 || Se != DCTSIZE2-1 || Ah != 0 || Al != 0)
  ERREXIT1(cinfo, JERR_BAD_PROG_SCRIPT, scanno);

Fixes issue 3916.

R=r
CC=golang-dev
http://codereview.appspot.com/6459052

tv42/old-go,gnanderson/go,gnanderson/go,dsriram/golang,dsriram/golang,tv42/old-go,dsriram/golang,dsriram/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,tv42/old-go,tv42/old-go,dsriram/golang,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,dsriram/golang,tv42/old-go,tv42/old-go,apparentlymart/golang,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,dsriram/golang,apparentlymart/golang