Merge pull request #434 from bwelling/immutable-rdata

Immutable rdata

diff --cc dns/rdata.py
Simple merge

diff --cc dns/rdtypes/ANY/HIP.py
Simple merge

diff --cc dns/rdtypes/ANY/NSEC.py
Simple merge

diff --cc dns/rdtypes/ANY/RP.py
Simple merge

diff --cc dns/rdtypes/ANY/RRSIG.py
Simple merge

diff --cc dns/rdtypes/ANY/SOA.py
Simple merge

diff --cc dns/rdtypes/CH/A.py
Simple merge

diff --cc dns/rdtypes/IN/IPSECKEY.py
Simple merge

diff --cc dns/rdtypes/IN/NAPTR.py
Simple merge

diff --cc dns/rdtypes/IN/PX.py
Simple merge

diff --cc dns/rdtypes/IN/SRV.py
Simple merge

diff --cc dns/rdtypes/mxbase.py
Simple merge

diff --cc dns/rdtypes/nsbase.py
Simple merge