[MEDIUM] signals: add support for registering functions and tasks

The two new functions below make it possible to register any number
of functions or tasks to a system signal. They will be called in the
registration order when the signal is received.

    struct sig_handler *signal_register_fct(int sig, void (*fct)(struct sig_handler *), int arg);
    struct sig_handler *signal_register_task(int sig, struct task *task, int reason);
diff --git a/include/types/task.h b/include/types/task.h
index 41f889c..405404b 100644
--- a/include/types/task.h
+++ b/include/types/task.h
@@ -1,23 +1,23 @@
 /*
-  include/types/task.h
-  Macros, variables and structures for task management.
-
-  Copyright (C) 2000-2009 Willy Tarreau - w@1wt.eu
-  
-  This library is free software; you can redistribute it and/or
-  modify it under the terms of the GNU Lesser General Public
-  License as published by the Free Software Foundation, version 2.1
-  exclusively.
-
-  This library is distributed in the hope that it will be useful,
-  but WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-  Lesser General Public License for more details.
-
-  You should have received a copy of the GNU Lesser General Public
-  License along with this library; if not, write to the Free Software
-  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
-*/
+ * include/types/task.h
+ * Macros, variables and structures for task management.
+ *
+ * Copyright (C) 2000-2010 Willy Tarreau - w@1wt.eu
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, version 2.1
+ * exclusively.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
 
 #ifndef _TYPES_TASK_H
 #define _TYPES_TASK_H
@@ -44,6 +44,12 @@
                            TASK_WOKEN_IO|TASK_WOKEN_SIGNAL|TASK_WOKEN_MSG| \
                            TASK_WOKEN_RES)
 
+/* Additional wakeup info may be passed in the state by lef-shifting the value
+ * by this number of bits. Not more than 8 bits are guaranteed to be delivered.
+ * System signals may use that too.
+ */
+#define TASK_REASON_SHIFT 8
+
 /* The base for all tasks */
 struct task {
 	struct eb32_node wq;		/* ebtree node used to hold the task in the wait queue */