c.h #includes a number of core libc header files, such as <stdio.h>.
There's no point in re-including these after having read postgres.h,
postgres_fe.h, or c.h; so remove code that did so.
While at it, also fix some places that were ignoring our standard pattern
of "include postgres[_fe].h, then system header files, then other Postgres
header files". While there's not any great magic in doing it that way
rather than system headers last, it's silly to have just a few files
deviating from the general pattern. (But I didn't attempt to enforce this
globally, only in files I was touching anyway.)
I'd be the first to say that this is mostly compulsive neatnik-ism,
but over time it might save enough compile cycles to be useful.
1. Don't #include postgres.h in a frontend build.
2. Don't assume that the backend's symbol PGSQL_AF_INET6 has anything to do
with the constant that will be used by system library functions (because,
in point of fact, it usually doesn't). Fortunately, PGSQL_AF_INET is equal
to AF_INET, so we can just cater for both sets of values in one case
construct without fear of conflict.
supplied, also print the IP address. This allows IPv4 and IPv6 failures
to be distinguished. Also useful when a hostname resolves to multiple
IP addresses.
Also, remove use of inet_ntoa() and use our own inet_net_ntop() in all
places, including in libpq, because it is thread-safe.
