The lexer variant also uses the string parser eventually (for now).

Also:
* document new_rdata_factory_users[] with an example
* Rename new_rdatafactory_users[] to new_rdata_factory_users[]

Also code to gen-rdatacode.py to optionally use the new RdataFactory
for some types if configured to do so.

Also have a default implementation that simply concatenates
all token data into a string and calls the create() variant
which accepts a string.

It just contains MasterLoader::Options enum for now.

Cppcheck complained there's an uninitialized variable in constructor.
This is mostly a false positive (the value is not used before being
assigned), but fix it anyway to make it silent.

These make distcheck fail on a number of systems (they have built-in disabling code for a number of other systems). See ticket #2479

Conflicts:
	src/lib/datasrc/datasrc_messages.mes

Also adjust affected tests accordingly.