Dear friends of ip addresses, I made something:

refactor dup code, minor janitoring, bump coverage

- remove duplicate netmask/hostmask code (it was identical in ipv4address & interface)
- make two ifs more pythonic
- Refactor and fix packed property for ipv6 addresses and networks. Apparently
  nobody has ever used this. :)
- Test coverage is now at 97%, the rest are mostly unreachable safeguards.

Please have a look at it if you will. The test suite passes of course.

That said, I'm pretty sure the constructor for IPv6Network is broken (particularly constructing from int and packed – also the the strict tests in these two cases don't make any sense as net mask is always ALL_ONES).

I'll be dreaming of ip addresses tonight. ;)