At least its basic version. Error handling must still be tested and done.

This is test for the ZoneLoader and its variant for testing copying
between two data sources. It includes some testing setups and mocks to
be reused in following tests.

Doesn't compile, undefined references to the tested methods.

Including documentation.

Reject invalid parameters and invalid attempts to load twice.

By catching all exceptions. It is questionable, if we want to do it that
way, but it seems to work at least for now.

Generate several broken input and see all of them fail. Also check they
continue to parse or not according to parameters.

Tested at least on the domain names. There is no known Rdata type
implementation handling relative names right now.

As we pass exactly one RR each time, RRset is overkill. We just pass
bunch of parameters to the callback.

It seemed the wrong pushSource was used due to some automatic
conversion. Also, it complained it couldn't find the file, because a
slash was missing (and nobody noticed before).

And fill it into the rrset.

This was from the template in trac and it is currently not needed.

The tentative interface of the MasterLoader was missing a callback to
add RRsets.

Also, include some small changes to the interface - pass RRClass as
reference and have DEFAULT options value for no special options.

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.