lzma tarball support

[Vincent Lefevre]

Hi,

Some packages are now distributed with lzma compression instead of bzip2,
e.g. texinfo 4.12:

  http://ftp.gnu.org/gnu/texinfo/

Going back to gzip would be a regression, in particular there is a big
size difference (here 2.4 MB for gzip, 1.3 MB for lzma).

What changes does a Portfile need to select lzma?

-- 
Vincent Lefèvre <vincent at vinc17.org> - Web: <http://www.vinc17.org/>
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Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)