Spf3

* Fix another bug in SPF record parsing that caused records with terms
separated by multple spaces as invalid, but they are fine per the ABNF
* Downcase names in additional answers returned by DNS before adding
to cache, since case inconsistency can cause PTR match failures (initial
patch thanks to Joni Fieggen) and other problems.

* Fix bug in SPF record parsing that caused all 'whitespace' characters to
be considered valid term separators and not just spaces
* Fixed multiple bugs in temperror processing that would lead to tracebacks
instead of correct error processing
* Fix AAAA not flagged as bytes when strict=2
* Include '~' as safe char in url quoted macro expansion

* Update for new SPF standards track RFC 7208
- Add processing for new void lookups processing limit
- Default SPF process timeout limit to 20 seconds per RFC 7208 4.6.4
- Change default DNS timeout to 20 seconds in DNSLookup to better match
RFC 7208 4.6.4
- Make mx lookups > 10 a permerror per RFC 7208 and mx-limit test
- Add RFC 7208 specific test suite and make allowance for RFC 7208 changes
in RFC 4408 test suite
- Convert YAML tests to TestCases, and have testspf.py return success/fail.

* Use ipaddr/ipaddres module in place of custom IP processing code
* Numerous python3 compatibility fixes
* Improved unicode error detection in SPF records
* Fixed a bug caused by a null CNAME in cache

* Allow for timeouts to be global for all DNS lookups instead of per DNS lookup
to allow for MAY processing time limitsin RFC 4408 10.1. See README for
details.
* Use openspf.net for SPF web site instead of openspf.org
* Extend query.get_header to return either Received-SPF (still default) or
RFC 5451 Authentication Results headers (needs authres 0.3 or later)
* Rework query.parse_header:
- Make query.parse_header automatically select Received-DPF or
Authentication Results header types and use them to collect SPF
results from trusted relays
- Add query.parse_header_spf and query.parse_header_ar functions for
header type specific processing
* Finish Python3 port - works with python2.6/2.7/3.2 and 2to3 is no longer
required - will also work with newer py3dns where TXT records are returned
as type bytes and not strings
* Accounts for new py3dns error classes coming in py3dns 3.0.2 (but fully
backward compatible with earlier versions)
* check for 7-bit ascii on TXT and SPF records
* fix CNAME chain duplicating TXT records

* Refactor code so that 2to3 will provide a working python3 module - Now
requires at least python2.6
* Update spfquery.py, type99.py, and testspf.py to work with either python or
python3 (2to3 not needed for these scripts)
- SPF test suite can now be run from either python or python3
* Ensure Temperror for all DNS rcodes other than 0 and 3 per RFC 4408
* Parse Received-SPF header
* Report CIDR error only for valid mechanism
* Handle invalid SPF record on command line
* Add timeout to check2