Secure Unix-domain sockets of "make check" temporary clusters.

Any OS user able to access the socket can connect as the bootstrap
superuser and proceed to execute arbitrary code as the OS user running
the test.  Protect against that by placing the socket in a temporary,
mode-0700 subdirectory of /tmp.  The pg_regress-based test suites and
the pg_upgrade test suite were vulnerable; the $(prove_check)-based test
suites were already secure.  Back-patch to 8.4 (all supported versions).
The hazard remains wherever the temporary cluster accepts TCP
connections, notably on Windows.

As a convenient side effect, this lets testing proceed smoothly in
builds that override DEFAULT_PGSOCKET_DIR.  Popular non-default values
like /var/run/postgresql are often unwritable to the build user.

Security: CVE-2014-0067

contrib/pg_upgrade/test.sh

@@ -15,14 +15,43 @@ set -e
 : ${PGPORT=50432}
 export PGPORT
 
+# Establish how the server will listen for connections
 testhost=`uname -s`
 
 case $testhost in
-	MINGW*)	LISTEN_ADDRESSES="localhost" ;;
-	*)		LISTEN_ADDRESSES="" ;;
+	MINGW*)
+		LISTEN_ADDRESSES="localhost"
+		PGHOST=""; unset PGHOST
+		;;
+	*)
+		LISTEN_ADDRESSES=""
+		# Select a socket directory.  The algorithm is from the "configure"
+		# script; the outcome mimics pg_regress.c:make_temp_sockdir().
+		PGHOST=$PG_REGRESS_SOCK_DIR
+		if [ "x$PGHOST" = x ]; then
+			{
+				dir=`(umask 077 &&
+					  mktemp -d /tmp/pg_upgrade_check-XXXXXX) 2>/dev/null` &&
+				[ -d "$dir" ]
+			} ||
+			{
+				dir=/tmp/pg_upgrade_check-$$-$RANDOM
+				(umask 077 && mkdir "$dir")
+			} ||
+			{
+				echo "could not create socket temporary directory in \"/tmp\""
+				exit 1
+			}
+
+			PGHOST=$dir
+			trap 'rm -rf "$PGHOST"' 0
+			trap 'exit 3' 1 2 13 15
+		fi
+		export PGHOST
+		;;
 esac
 
-POSTMASTER_OPTS="-F -c listen_addresses=$LISTEN_ADDRESSES"
+POSTMASTER_OPTS="-F -c listen_addresses=$LISTEN_ADDRESSES -k \"$PGHOST\""
 
 temp_root=$PWD/tmp_check
 
@@ -79,7 +108,6 @@ PGSERVICE="";         unset PGSERVICE
 PGSSLMODE="";         unset PGSSLMODE
 PGREQUIRESSL="";      unset PGREQUIRESSL
 PGCONNECT_TIMEOUT=""; unset PGCONNECT_TIMEOUT
-PGHOST="";            unset PGHOST
 PGHOSTADDR="";        unset PGHOSTADDR
 
 logdir=$PWD/log