[krbdev.mit.edu #8424] New failure in t_sn2princ.py

[Greg Hudson via RT]

What version is this?  As far as I can tell, t_sn2princ.py has always 
checked the reverse resolution results before running the test, so it 
should skip the test rather than failing.

(The PTR change is intentional.  https://github.com/krb5/krb5/pull/457 
revises the test to be less specific about the reverse resolution result, 
but it should not be required for the test script to succeed.)