Problem: Item_char_typecast reported wrong max_length when
casting to BINARY, which lead, in particular, in wrong
"ORDER BY BINARY(char_column)" results.

Fix: making Item_char_typecast report correct max_length.

  @ mysql-test/r/ctype_utf16.result
    Fixing old incorrect test result.
  @ mysql-test/r/ctype_utf32.result
    Fixing old incorrect test result.
  @ mysql-test/r/ctype_utf8.result
    Adding new test
  @ mysql-test/t/ctype_utf8.test
    Adding new test
  @ sql/item_timefunc.cc
    Making Item_char_typecast report correct max_length
    when cast is done to BINARY.