Fix signedness warning in rsa_keypair_to_openpgp.

ChangeLog

 2016-08-16  Niels Möller  <nisse@lysator.liu.se>
 
+	* rsa2openpgp.c (rsa_keypair_to_openpgp): Added cast to const
+	uint8_t *.
+
 	* pgp-encode.c (write_string): New helper function, replacing...
 	(WRITE): ... deleted macro.
 

rsa2openpgp.c

@@ -85,7 +85,7 @@ rsa_keypair_to_openpgp(struct nettle_buffer *buffer,
 
   /* userid packet */
   userid_start = buffer->size;
-  if (!pgp_put_userid(buffer, strlen(userid), userid))
+  if (!pgp_put_userid(buffer, strlen(userid), (const uint8_t *) userid))
     return 0;
 
   /* FIXME: We hash the key first, and then the user id. Is this right? */