gpg: Use higher-level functions.

* g10/build-packet.c (do_symkey_enc): Use iobuf_write instead of
iobuf_put in a loop.  Use iobuf_copy instead of iobuf_read and
iobuf_write in a loop.  Move the memory wiping from here...
* common/iobuf.c (iobuf_copy): ... to here.

--
Signed-off-by: Neal H. Walfield <neal@g10code.com>

common/iobuf.c

@@ -2253,6 +2253,9 @@ iobuf_copy (iobuf_t dest, iobuf_t source)
         break;
       nwrote += nread;
     }
+
+  /* Burn the buffer.  */
+  wipememory (temp, sizeof (temp));
   xfree (temp);
 
   return nwrote;