[krbdev.mit.edu #7124] krb5_sname_to_principal canonicalization should work with IPv6-only hosts

[Greg Hudson via RT]

Some more information on the underlying getaddrinfo issue:

* The attached test program can be used to demonstrate the issue.

* On Ubuntu 12.04 or 12.10, getaddrinfo appears to do a PTR lookup for 
ai_canonname if given either the AI_ADDRCONFIG flag is specified or an 
address family is given in the hint.  On test versions of Ubuntu 13.04, 
the AI_ADDRCONFIG flag doesn't appear to cause the PTR lookup, but an 
address family still does.

* Unmodified glibc master sources (as of today) match the Ubuntu 13.04 
behavior.  This is not surprising as 13.04 is based on eglibc 2.17.

* Unmodified glibc 2.15 sources *also* match the Ubuntu 13.04 behavior.  
This is surprising to me, because Ubuntu 12.04 and 12.10 are based on 
eglibc 2.15, and I haven't been able to find a relevant change in either 
eglibc or in the Ubuntu package's patches.

* I reported the AF_INET part of the problem upstream: http://sourceware.org/bugzilla/show_bug.cgi?id=15218