Re-add old Xinerama code for the poor nvidia users

Add --force-xinerama when starting i3 to use Xinerama instead of RandR.
This should *ONLY* be done if you have no other choice (nvidia’s
binary driver uses twinview and does not expose the monitor information
through RandR).

include/xinerama.h

@@ -0,0 +1,23 @@
+/*
+ * vim:ts=8:expandtab
+ *
+ * i3 - an improved dynamic tiling window manager
+ *
+ * © 2009-2010 Michael Stapelberg and contributors
+ *
+ * See file LICENSE for license information.
+ *
+ */
+#include "data.h"
+
+#ifndef _XINERAMA_H
+#define _XINERAMA_H
+
+/**
+ * We have just established a connection to the X server and need the initial
+ * Xinerama information to setup workspaces for each screen.
+ *
+ */
+void initialize_xinerama(xcb_connection_t *conn);
+
+#endif