Previously, we included <xlocale.h> only if necessary to get the definition
of type locale_t.  According to notes in PGAC_TYPE_LOCALE_T, this is
important because on some versions of glibc that file supplies an
incompatible declaration of locale_t.  (This info may be obsolete, because
on my RHEL6 box that seems to be the *only* definition of locale_t; but
there may still be glibc's in the wild for which it's a live concern.)

It turns out though that on FreeBSD and maybe other BSDen, you can get
locale_t from stdlib.h or locale.h but mbstowcs_l() and friends only from
<xlocale.h>.  This was leaving us compiling calls to mbstowcs_l() and
friends with no visible prototype, which causes a warning and could
possibly cause actual trouble, since it's not declared to return int.

Hence, adjust the configure checks so that we'll include <xlocale.h>
either if it's necessary to get type locale_t or if it's necessary to
get a declaration of mbstowcs_l().

Report and patch by Aleksander Alekseev, somewhat whacked around by me.
Back-patch to all supported branches, since we have been using
mbstowcs_l() since 9.1.

This function is pervasive on free software operating systems; import
NetBSD's implementation.  Back-patch to 8.4, like the commit that will
harness it.

We previously supposed that any given platform would supply both or neither
of these functions, so that one configure test would be sufficient.  It now
appears that at least on AIX this is not the case ... which is likely an
AIX bug, but nonetheless we need to cope with it.  So use separate tests.
Per bug #6758; thanks to Andrew Hastie for doing the followup testing
needed to confirm what was happening.

Backpatch to 9.1, where we began using these functions.

These should have been removed when the BeOS port was removed in
44f90212.

These should not be needed anymore, at least after the recent port
removals.  So let's see whether we can do without them.

In the Fedora variant of MinGW, the openssl libraries have their normal
names, not libeay32 and libssleay32.  Adjust configure probes to allow
that, per bug #6486.

Tomasz Ostrowski

All supported platforms support the C89 standard function atexit()
(SunOS 4 probably being the last one not to), and supporting both
makes the code clumsy.

This lie has been harmless until now, but has been exposed by the
change to include postgres.h before the python headers, which
in some versions include inttypes.h if HAVE_INTTYPES_H is set.

Per gripe from Tom Lane. I have tested this with VC 2008, and assume
it will work with earlier versions.

It turns out the reason we hadn't found out about the portability issues
with our credential-control-message code is that almost no modern platforms
use that code at all; the ones that used to need it now offer getpeereid(),
which we choose first.  The last holdout was NetBSD, and they added
getpeereid() as of 5.0.  So far as I can tell, the only live platform on
which that code was being exercised was Debian/kFreeBSD, ie, FreeBSD kernel
with Linux userland --- since glibc doesn't provide getpeereid(), we fell
back to the control message code.  However, the FreeBSD kernel provides a
LOCAL_PEERCRED socket parameter that's functionally equivalent to Linux's
SO_PEERCRED.  That is both much simpler to use than control messages, and
superior because it doesn't require receiving a message from the other end
at just the right time.

Therefore, add code to use LOCAL_PEERCRED when necessary, and rip out all
the credential-control-message code in the backend.  (libpq still has such
code so that it can still talk to pre-9.1 servers ... but eventually we can
get rid of it there too.)  Clean up related autoconf probes, too.

This means that libpq's requirepeer parameter now works on exactly the same
platforms where the backend supports peer authentication, so adjust the
documentation accordingly.

These functions should take a pg_locale_t, not a collation OID, and should
call mbstowcs_l/wcstombs_l where available.  Where those functions are not
available, temporarily select the correct locale with uselocale().

This change removes the bogus assumption that all locales selectable in
a given database have the same wide-character conversion method; in
particular, the collate.linux.utf8 regression test now passes with
LC_CTYPE=C, so long as the database encoding is UTF8.

I decided to move the char2wchar/wchar2char functions out of mbutils.c and
into pg_locale.c, because they work on wchar_t not pg_wchar_t and thus
don't really belong with the mbutils.c functions.  Keeping them where they
were would have required importing pg_locale_t into pg_wchar.h somehow,
which did not seem like a good plan.

There is not yet support in initdb to populate the pg_collation
catalog, but if that is done manually, the rest should work.