fixing tests accordingly
item.cc:
  Bug #10892 user variables not auto cast for comparisons
  When mixing strings with different character sets,
  and coercibility is the same, we allow conversion
  if one character set is superset for other character set.


sql/item.cc:
  Bug #10892 user variables not auto cast for comparisons
  When mixing strings with different character sets,
  and coercibility is the same, we allow conversion
  if one character set is superset for other character set.
mysql-test/t/grant.test:
  fixing tests accordingly
mysql-test/r/grant.result:
  fixing tests accordingly