keyfile: clean up directory structure

The IO library was in io/ because I was too lazy to find autotools'
SUBDIRS rules at the time and that you could use '.' for the current
directory.  Fix that and use its own error defines instead of
the system settings service.  Clean up a for more things for good
measure too (like KEYFILE_DIR, etc).

system-settings/plugins/keyfile/reader.h

@@ -0,0 +1,30 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: t; c-basic-offset: 4 -*- */
+/* NetworkManager system settings service - keyfile plugin
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Copyright (C) 2008 Novell, Inc.
+ * Copyright (C) 2008 Red Hat, Inc.
+ */
+
+#ifndef _KEYFILE_PLUGIN_READER_H
+#define _KEYFILE_PLUGIN_READER_H
+
+#include <glib.h>
+#include <nm-connection.h>
+
+NMConnection *connection_from_file (const char *filename, GError **error);
+
+#endif /* _KEYFILE_PLUGIN_READER_H */