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 - no longer builds src/lib/dns/python directory
 - gen-rdatacode.py is no longer necessary for build

Also, updated configure.ac to not reference removed files. The
--disable-dhcp and --disable-dns configuration flags have been removed.

In #3170 where parallel builds were fixed, some of the dependencies
for running gen-rcodedata.py were not correctly set. Thus a file could
be changed but nothing rebuilt. Fix that.

This reverts commit f2f02dba.
other commit reportedly addressed the issue that this hack tries to solve.

added some tests to check the definitions are complete and correct.

now some parameters for ANY, AXFR, IXFR types and NONE class are
auto-generated, and corresponding hardcoding was removed.

specifically, it generates code to create RRType and RRClass constants.

this is especially useful for tests.

these are (indirectly) necessary for building external programs.

It just contains MasterLoader::Options enum for now.

Fixing merge conflicts:
	src/lib/dns/master_lexer.cc