
add statics for RRClass::IN() (RRClass.IN()) etc.
(and replace RRClass("IN") in tests with those)

same for RRType? (xfrout.py.in line 256)

creating a render message and not setting opcode/rcode results in a segfault later (nullpointer)
(is this cpp or python problem?)

The function set wrapped is not complete; for instance, in
MessageRenderer, we really only provide the high-level readout
functions. Do we need access to the writers? (there is one set() right
now).

segfault when comparing with bad type like int (at least for Name and Rcode, but probably for the rest too)
