Changed long packat handling to check for packets of length 0xffffff.
This does however break packet handling for older clients.
If you are using packets >= 16M then you need to upgrade client and server
after this patch.


Docs/internals.texi:
  Updated documentation for 4.1 protocol
sql/ha_innodb.cc:
  Optimization of checking command
sql/item.h:
  Removed automatic set of length for Item_string
sql/item_create.cc:
  Optimized create of create_func_current_user()
sql/net_serv.cc:
  Fixed wrong max packet length
sql/sql_acl.cc:
  Safety fix.
sql/sql_parse.cc:
  Cut hostnames at HOSTNAME_LENGTH to avoid theoretical hostname overruns