telnet client: fix unexisting reference to engine.slots
Merge pull request #464 from kalessin/telnet

telnet client: fix unexisting reference to engine.slots
Deprecate body_or_str helper function only used by xml iterators
Do not call body_as_unicode on non text responses. closes #462
lxml is required, no need to skip tests.
add a tox env for Python 3.3