Map unknown realm errors to PAM_AUTHINFO_UNAVAIL

Map unknown realm errors from the Kerberos libraries to the PAM error
code PAM_AUTHINFO_UNAVAIL instead of PAM_AUTH_ERR.
Update tests/pam-util/vector-t.c from rra-c-util

Fixes compilation errors with make warnings under gcc 4.9 by fixing
the formats and casts.  Also avoids using snprintf in favor of using
basprintf.