sql/item.cc:
  don't forget to adjust the length of the string when removing leading spaces
sql/sql_acl.cc:
  when updating the hostname of the ACL_USER, update the hostname_length too
sql/sql_parse.cc:
  first compare the username string, then test the host pointer
  (host pointer is undefined when the username string is one of the hard-coded values
  set by the parser). This is not a bug, old code is perfectly safe as the undefined
  host pointer is never dereferenced, but let's keep valgrind happy.