libfdt: Make fdt_check_header() public

Changed _fdt_check_header() to fdt_check_header() and made it part of
the interface - it is a useful routine.

Also did some asthetics cleanup to the include files (headers).

include/libfdt_env.h

@@ -1,3 +1,23 @@
+/*
+ * libfdt - Flat Device Tree manipulation (build/run environment adaptation)
+ * Copyright (C) 2007 Gerald Van Baren, Custom IDEAS, vanbaren@cideas.com
+ * Original version written by David Gibson, IBM Corporation.
+ *
+ * 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; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * 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 St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
 #ifndef _LIBFDT_ENV_H
 #define _LIBFDT_ENV_H