to a "hidden" _dns module with a frontend .py module.  It will make it easier
to handle objects defined in pydnspp.  no functional change at this moment.
note that we need to allow classes in the module to be subclassed.

it's always NULL because it cannot be configured with TSIG keys.
it should be done in a separate ticket.

NameCheck<RequestContext>::matches using that support.

values for socket.getaddrinfo().
commiting and pushing it at my discretion.

Conflicts:
	src/bin/xfrout/tests/xfrout_test.py.in

quickly discussed on jabber.

suggested in review.

LIBRARY_PATH_PLACEHOLDER

which is not (at least yet) applicable.  also added a note about the
difference between the C++ doc and the python version derived from it.

This is not directly related to the subject of this ticket, but
would be necessary to complete the TSIG + TC bit support.