mysql-test/r/ctype_collate.result:
  NO COLLATION has less coercibility than IMPLICIT and COERCIBLE
sql/item.cc:
  Function to choose collation for dyadic operations
sql/item.h:
  NO COLLATION has less coercibility than IMPLICIT and COERCIBLE
sql/item_func.cc:
  Function to choose collation for dyadic operations
sql/item_strfunc.cc:
  Function to choose collation for dyadic operations
sql/item_strfunc.h:
  Use arg's attributes