not directly related to this task, but I found we need one real (non wrapper)
example to test some of the feature of generic createRdata().

also updated RDATA template including with-lexer constructor.

an empty qstring previously caused an exception, which is a clear bug
and should be fixed.  nul-terminating string regions is an extension,
but I found it useful when implementing RDATA parsers.

Removed the socket.shutdown() before socket.close() again, this seemed to cause some errors with the statistics tests (which we will look into separately)

Discussed on jabber

for consistency; it's awkward to see it as a struct while LexerError as a
.class.

The choice is basically a matter of taste, but I personally think it's
better to be defined as a class as its base is defined as a class, and
these exception structs are not just a trivial set of values.