Beginning a DEP5 debian/copyright parsing module

[John Wright]

This is the first few patches of a series to add a copyright module for
parsing DEP5-format debian/copyright files.  There is still more work to do
(basically this just parses the header paragraph, but it lays the foundation
for the rest of the module and hopefully more to come).  I'm hoping for
comments on the approach, since it's different from what we've done for
previous 822-like things in the past (it wraps a "raw" Deb822 object instead
of subclassing Deb822 and changing how certain fields are stored).  I think
it's a better pattern, and I wish we had used something more like it
before...

This is also available on alioth:
http://anonscm.debian.org/cgit/pkg-python-debian/python-debian.git/log/?h=jsw/dep5-copyright

If you pull that branch, be aware that I will be rewriting history there -
it's just for review convenience.

Thanks!