patch 7.4.804

Problem:    Xxd doesn't have a license notice.
Solution:   Add license as indicated by Juergen.

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    804,
 /**/
     803,
 /**/

src/xxd/xxd.c

@@ -55,6 +55,9 @@
  *
  * (c) 1990-1998 by Juergen Weigert (jnweiger@informatik.uni-erlangen.de)
  *
+ * I hereby grant permission to distribute and use xxd
+ * under X11-MIT or GPL-2.0 (at the user's choice).
+ *
  * Small changes made afterwards by Bram Moolenaar et al.
  *
  * Distribute freely and credit me,