points. For library functions, the pattern is __sleep() <--
_libc_sleep() <-- sleep(). The arrows represent weak aliases. For
system calls, the pattern is _read() <-- _libc_read() <-- read().
(1)added error check of if_nameindex() return value at getaddrinfo().
(2)print out more detailed information when getaddrinfo() error value
is EAI_SYSTEM.(in this case system error num is kept in errno)
(1) is Discovered by: jinmei@kame.net in KAME environment.
