[twill] dirstack extension module

[Titus Brown]

Hi all,

I just added the dirstack extension module; current docs here:

	http://issola.caltech.edu/~t/twill/doc/extensions.html#dirstack-manipulate-the-current-working-directory-cwd

As you might guess, it lets you manipulate the current working
directory!

It's in the latest darcs and the latest .tar.gz, but I didn't bother
building an egg for it yet.

cheers,
--titus