total variation denoising

[Emmanuelle Gouillart]

	Dear all,

	I finally found some time to do some polishing on the TV
denoising code that Ma�l had written a while ago. I added a new module to
my branch https://github.com/emmanuelle/scikits.image/tree/tv_denoise  
(https://github.com/emmanuelle/scikits.image/blob/tv_denoise/scikits/image/filter/tv_denoise.py).

	I'd like to have your opinion on how the code could be improved
before a pull request.

	Cheers,

	Emmanuelle