Fix example/gzappend.c for proper z_const usage.

examples/gzappend.c

 /* gzappend -- command to append to a gzip file
 
-  Copyright (C) 2003 Mark Adler, all rights reserved
-  version 1.1, 4 Nov 2003
+  Copyright (C) 2003, 2012 Mark Adler, all rights reserved
+  version 1.2, 13 Aug 2012
 
   This software is provided 'as-is', without any express or implied
   warranty.  In no event will the author be held liable for any damages
@@ -39,6 +39,7 @@
  *                      - Keep gzip file clean on appended file read errors
  *                      - Use in-place rotate instead of auxiliary buffer
  *                        (Why you ask?  Because it was fun to write!)
+ * 1.2  13 Aug 2012     - Fix for proper z_const usage
  */
 
 /*
@@ -170,7 +171,7 @@ typedef struct {
     int size;                   /* 1 << size is bytes in buf */
     unsigned left;              /* bytes available at next */
     unsigned char *buf;         /* buffer */
-    unsigned char *next;        /* next byte in buffer */
+    z_const unsigned char *next;    /* next byte in buffer */
     char *name;                 /* file name for error messages */
 } file;
 
@@ -467,7 +468,7 @@ int main(int argc, char **argv)
     z_stream strm;
 
     /* ignore command name */
-    argv++;
+    argc--; argv++;
 
     /* provide usage if no arguments */
     if (*argv == NULL) {