Add idle_in_transaction_session_timeout.

Vik Fearing, reviewed by Stéphane Schildknecht and me, and revised
slightly by me.

src/backend/utils/misc/guc.c

@@ -2065,6 +2065,17 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"idle_in_transaction_session_timeout", PGC_USERSET, CLIENT_CONN_STATEMENT,
+			gettext_noop("Sets the maximum allowed duration of any idling transaction."),
+			gettext_noop("A value of 0 turns off the timeout."),
+			GUC_UNIT_MS
+		},
+		&IdleInTransactionSessionTimeout,
+		0, 0, INT_MAX,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"vacuum_freeze_min_age", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Minimum age at which VACUUM should freeze a table row."),