getaddrinfo() for threading instead of gethostbyname()

When FreeBSD didn't have gethostbyname_r(), and gethostbyname() wasn't
thread-safe, Marc asked around and found out that the threaded solution
for this is to use getaddrinfo(). This makes sense because
getaddrinfo() is described as:

getaddrinfo () function is defined for protocol-independent nodename-
to-address translation. It performs functionality of gethostbyname(3)
and getservbyname(3), in more sophisticated manner.

A number of platforms have getpwuid_r(), but not gethostbyname_r(). I
now realize it is because they are assuming you arew using getaddrinfo(),
which has freeaddrinfo() to free the allocated memory in a thread-safe
manner.

Right now, we call gethostname() from two places:

port/getaddrinfo() (if backend)
port/thread.c::pqGethostbyname()

and pqGethostbyname() (thread-safe) is called only by:

port/getaddrinfo() (if frontend)
libpq/fe-secure.c

If we convert fe-secure.c to use getaddrinfo(), then all host address
lookups go through getaddrinfo().

Then, if we don't need our port/getaddrinfo(), we don't care about a
non-thread-safe gethostbyname() on that platform. This improves our
thread-safe support. Specifically, it prevents host name lookups from
be serialized by our pthread locks.

Once everything goes through getaddrinfo(), I will modify my thread test
program to test gethostbyname() threading _only_ if getaddrinfo()
doesn't exist.

--
Bruce Momjian | http://candle.pha.pa.us
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