Replaced sensible-browser with xdg-open (more cross-distro compatible)
Merge pull request #544 from Renelvon/master

Refactor and rewrite testsuite.
Merge pull request #546 from integers/master

Replaced sensible-browser with xdg-open (more cross-distro compatible)
Simplify __eq__; drop __ne__

Implementing both __eq__ and __ne__ is error prone.
As it should always be the case that
    (a != b) == not (a == b)
only one magic function is needed; the other will be provided
automatically.
A simple hash.
Implement repr; derive str automatically.

Implementing __str__ but not __repr__ is considered bad practice,
and makes debugging a bit awkward, because Python drops in a default
replacement for the missing __repr__. However, if only __repr__ is
implemented, then it will be used for both repr and str calls.
Unit tests for node/contact.py.