Fix the Avahi example

– Avahi normally listens on the system bus, use that instead of the
  session bus,
– code updated to the current python-tdbus API,
– enable logging (this helped finding one of the bugs in the code, as
  tdbus sends some error messages there).
Include examples and doc files in src distribution

The archive created by 'python setup.py sdist' should contain
the complete code, including the examples and the 'AUTHORS, HACKING,
LICENSE' files.
Merge pull request #2 from Jajcus/fix_avahi_example

Fix the Avahi example
Merge pull request #3 from Jajcus/sdist_manifest

Include examples and doc files in src distribution