[cairo] JPEG support patch

[Vladimir Vukicevic]

Andrew McRae wrote:
> Comments welcome on the addition of the JPEG
> support functions to the API.
> 
> Cheers,
> AMc
> PS to pre-empt the inevitable discussion on whether it is
> wise to add yet more image formats to cairo, clearly
> we need to support a small number of popular formats, and
> in IMHO this list should perhaps be PNG, JPEG and perhaps GIF.
> Someone suggested a separation of the image format I/O
> into a separate library - this is probably a good idea..

Pre-empting or not, I'm going to strongly disagree that support for more 
formats was needed.  PNG was added as a way to ease testing; that's it. 
  I'd be happy to see the PNG support become part of the testing 
boilerplate, instead of as part of the core library as well, but that 
might be harder to change now.  Adding more of this type of "optional" 
functionality to cairo just dilutes the API.

There are already a pile of pretty good image loading libraries (DevIL 
comes to mind) that will happily load into a cairo_image_surface_t -- if 
you think there's a need for yet another image loading library that's 
specifically tied to cairo, I'd say go for it, but please keep it out of 
cairo proper.

     - Vlad