ipc: implement GET_WORKSPACES message type

This is the foundation to use dzen2 or similar as a complete
replacement for the internal workspaces bar.

A testcase is included, more documentation about the IPC interface
will follow.

include/i3/ipc.h

@@ -3,7 +3,7 @@
  *
  * i3 - an improved dynamic tiling window manager
  *
- * © 2009 Michael Stapelberg and contributors
+ * © 2009-2010 Michael Stapelberg and contributors
  *
  * See file LICENSE for license information.
  *
@@ -15,10 +15,26 @@
 #ifndef _I3_IPC_H
 #define _I3_IPC_H
 
+/*
+ * Messages from clients to i3
+ *
+ */
+
 /** Never change this, only on major IPC breakage (don’t do that) */
 #define I3_IPC_MAGIC 			"i3-ipc"
 
 /** The payload of the message will be interpreted as a command */
-#define I3_IPC_MESSAGE_TYPE_COMMAND	0
+#define I3_IPC_MESSAGE_TYPE_COMMAND	        0
+
+/** Requests the current workspaces from i3 */
+#define I3_IPC_MESSAGE_TYPE_GET_WORKSPACES      1
+
+/*
+ * Messages from i3 to clients
+ *
+ */
+
+/** Workspaces reply type */
+#define I3_IPC_REPLY_TYPE_WORKSPACES            1
 
 #endif