[krbdev.mit.edu #1392] getaddrinfo wrapper not good enough on AIX

[Ken Raeburn via RT]

Donn Cave points out that AIX getaddrinfo returns a canonical-name field
that is allocated but not filled in.  Meanwhile, some of our code is
relying on that field being filled in.  The support for this case exists
in the wrapper code already, but is not turned on for AIX.  Simply
turning it on for AIX results in some problems because apparently it's
using yet a third interface for gethostbyname_r that we don't support,
so that will need to be worked around too.

Broken in 1.3a1, probably should be fixed for 1.3 beta at latest.