Fix for libpq compile

This commit caused my compile to fail on CVS HEAD:

    revision 1.399
    date: 2010/07/18 11:37:26;  author: petere;  state: Exp;  lines: +88 -1
    Add server authentication over Unix-domain sockets

    This adds a libpq connection parameter requirepeer that specifies the user
    name that the server process is expected to run under.

    reviewed by KaiGai Kohei

The problem is that the code was not checking for SO_PEERCRED.

I have applied the attached check, but without SO_PEERCRED I can't
report the username which failed.  Please adjust this if necessary.
Thanks.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + None of us is going to be here forever. +
Index: fe-connect.c
===================================================================
RCS file: /cvsroot/pgsql/src/interfaces/libpq/fe-connect.c,v
retrieving revision 1.399
diff -c -r1.399 fe-connect.c
*** fe-connect.c    18 Jul 2010 11:37:26 -0000    1.399
--- fe-connect.c    18 Jul 2010 15:47:32 -0000
***************
*** 1816,1823 ****
--- 1816,1827 ----
                      if (pass == NULL)
                      {
                          appendPQExpBuffer(&conn->errorMessage,
+ # if defined(SO_PEERCRED)
                                            libpq_gettext("local user with ID %d does not exist\n"),
                                                          (int) peercred.uid);
+ #else
+                                           libpq_gettext("matching local user does not exist\n"));
+ #endif
                          goto error_return;
                      }