Problem: Item_str_ascii_func::val_str() did not set
charset of the returned value properly.
  
  mysql-test/include/ctype_numconv.inc
  mysql-test/r/ctype_binary.result
  mysql-test/r/ctype_cp1251.result
  mysql-test/r/ctype_latin1.result
  mysql-test/r/ctype_ucs.result
  - Adding tests
  
  sql/item_strfunc.cc
  - Adding initialization of charset