Bug#612341: bumblebee, libjpeg-turbo: Wheezy does not work well with modern notebook PCs.

[Mathieu Malaterre <malat@debian.org>]

For information, it looks like not all of libjpeg8 is actually
implemented in libjpeg-turbo, ref:
http://libjpeg-turbo.svn.sourceforge.net/viewvc/libjpeg-turbo/trunk/README-turbo.txt

In particular:

libjpeg v7 and v8 Features:
---------------------------

Fully supported:

-- cjpeg: Separate quality settings for luminance and chrominance
   Note that the libpjeg v7+ API was extended to accommodate this feature only
   for convenience purposes.  It has always been possible to implement this
   feature with libjpeg v6b (see rdswitch.c for an example.)

-- libjpeg: IDCT scaling extensions in decompressor
   libjpeg-turbo supports IDCT scaling with scaling factors of 1/8, 1/4, 3/8,
   1/2, 5/8, 3/4, 7/8, 9/8, 5/4, 11/8, 3/2, 13/8, 7/4, 15/8, and 2/1 (only 1/4
   and 1/2 are SIMD-accelerated.)

-- cjpeg: 32-bit BMP support

-- jpegtran: lossless cropping

-- jpegtran: -perfect option

-- rdjpgcom: -raw option

-- rdjpgcom: locale awareness


Fully supported when using libjpeg v7/v8 emulation:

-- libjpeg: In-memory source and destination managers


Not supported:

-- libjpeg: DCT scaling in compressor
   cinfo.scale_num and cinfo.scale_denom are silently ignored.
   There is no technical reason why DCT scaling cannot be supported, but
   without the SmartScale extension (see below), it would only be able to
   down-scale using ratios of 1/2, 8/15, 4/7, 8/13, 2/3, 8/11, 4/5, and 8/9,
   which is of limited usefulness.

-- libjpeg: SmartScale
   cinfo.block_size is silently ignored.
   SmartScale is an extension to the JPEG format that allows for DCT block
   sizes other than 8x8.  It would be difficult to support this feature while
   retaining backward compatibility with libjpeg v6b.

-- libjpeg: Fancy downsampling in compressor
   cinfo.do_fancy_downsampling is silently ignored.
   This requires the DCT scaling feature, which is not supported.

-- jpegtran: Scaling
   This requires both the DCT scaling and SmartScale features, which are not
   supported.

-- Lossless RGB JPEG files
   This requires the SmartScale feature, which is not supported.