Fist threading support

[Almad]

Hi,

transformation in threads is now supported, see
http://projects.almad.net/pyarticle/browser/pyarticle/trunk/pyarticle/test/test_threading.py

I'd be glad to hear Your opinions to chosen API, as well as how to resolve
code duplication - see ticket #20
http://projects.almad.net/pyarticle/ticket/20

--
Almad