[krbdev.mit.edu #4114] no mechanism for timing out DNS lookups

[Russ Allbery <rra@stanford.edu> via RT]

It would be nice to be able to specify a timeout for doing DNS lookups
of, for instance, KDC IP addresses.  Right now, the library just calls
getaddrinfo and takes however long getaddrinfo takes.  When Kerberos
calls are done by a PAM module, this can result in login timeouts rather
than failover to local authentication.

Solving this problem will probably require using an asynchronous DNS
mechanism such as described in RT#1453.