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

d0f/go-zh,rdp/rogerpack2005-golang,scirelli/scirelli-go,mhennings/marcohennings-go,d0f/go-zh,d0f/go-zh,rdp/rogerpack2005-golang,scirelli/scirelli-go,sanjosh/sanjos100-tipc,bryanxu/go-zh,rdp/rogerpack2005-golang,bryanxu/go-zh,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,scirelli/scirelli-go,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,sanjosh/sanjos100-tipc,scirelli/scirelli-go,scirelli/scirelli-go,rdp/rogerpack2005-golang,mhennings/marcohennings-go,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,scirelli/scirelli-go,webfd/go-zh,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,mhennings/marcohennings-go,scirelli/scirelli-go,rflanagan/reginaldflanagan-project1,bryanxu/go-zh,glycerine/jeaten-go-arrayof-structof,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,d0f/go-zh,rdp/rogerpack2005-golang,bryanxu/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,d0f/go-zh,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,webfd/go-zh,scirelli/scirelli-go,d0f/go-zh,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,webfd/go-zh,mhennings/marcohennings-go,glycerine/jeaten-go-arrayof-structof,bryanxu/go-zh,bryanxu/go-zh,mhennings/marcohennings-go,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,rflanagan/reginaldflanagan-project1,rflanagan/reginaldflanagan-project1