Checking if xxCOUNT corresponds to the content.

- Trailing garbage (i.e. more data than expected from the xxCOUNT)
  is ignored and the packet is processed as if there were no such
  data. (This behaviour may change later according to other servers
  - see #1336).
- If the packet contains less data then expected (xxCOUNT larger
  then real count of RRs in the corresponding section), FORMERR
  is returned.

refs #1333 @1h