Fix Minnich's Copyrights

As far as I can remember the new `dc` argument added to the `mount`
system call is the only API innovation that I imported from Harvey-OS
in the Jehanne's kernel.

It's a great idea of Ronald G. Minnich, introduced at

	72777a1fab

Since he didn't amended the copyright statements in Harvey, I forgot
to amend it here.

Sorry, my fault.

sys/src/kern/boot/boot.c

@@ -4,6 +4,9 @@
 /* Portions of this file are Copyright (C) 2015-2018 Giacomo Tesio <giacomo@tesio.it>
  * See /doc/license/gpl-2.0.txt for details about the licensing.
  */
+/* Portions of this file are Copyright (C) 2015 Ronald G. Minnich <rminnich@gmail.com>
+ * See /doc/license/gpl-2.0.txt for details about the licensing.
+ */
 
 #include <u.h>
 #include <libc.h>

sys/src/kern/port/lib.h

@@ -1,3 +1,13 @@
+/* Copyright (C) Charles Forsyth
+ * See /doc/license/NOTICE.Plan9-9k.txt for details about the licensing.
+ */
+/* Portions of this file are Copyright (C) 2015-2018 Giacomo Tesio <giacomo@tesio.it>
+ * See /doc/license/gpl-2.0.txt for details about the licensing.
+ */
+/* Portions of this file are Copyright (C) 2015 Ronald G. Minnich <rminnich@gmail.com>
+ * See /doc/license/gpl-2.0.txt for details about the licensing.
+ */
+
 /*
  * functions (possibly) linked in, complete, from libc.
  */

sys/src/kern/port/sysfile.c

@@ -4,6 +4,9 @@
 /* Portions of this file are Copyright (C) 2015-2018 Giacomo Tesio <giacomo@tesio.it>
  * See /doc/license/gpl-2.0.txt for details about the licensing.
  */
+/* Portions of this file are Copyright (C) 2015 Ronald G. Minnich <rminnich@gmail.com>
+ * See /doc/license/gpl-2.0.txt for details about the licensing.
+ */
 #include	"u.h"
 #include	"../port/lib.h"
 #include	"mem.h"