Problems:
      - regression (compating to version 5.1) in metadata for BLOB types
      - inconsistency between length metadata in server and embedded for BLOB types
      - wrong max_length calculation in items derived from BLOB columns
     @ libmysqld/lib_sql.cc
        Calculating length metadata in embedded similary to server version,
        using new function char_to_byte_length_safe().
     @ mysql-test/r/ctype_utf16.result
        Adding tests
     @ mysql-test/r/ctype_utf32.result
        Adding tests
     @ mysql-test/r/ctype_utf8.result
        Adding tests
     @ mysql-test/r/ctype_utf8mb4.result
        Adding tests
     @ mysql-test/t/ctype_utf16.test
        Adding tests
     @ mysql-test/t/ctype_utf32.test
        Adding tests
     @ mysql-test/t/ctype_utf8.test
        Adding tests
     @ mysql-test/t/ctype_utf8mb4.test
        Adding tests
     @ sql/field.cc
        Overriding char_length() for Field_blob:
        unlike in generic Item::char_length() we don't
        divide to mbmaxlen for BLOBs.
     @ sql/field.h
        - Making Field::char_length() virtual
        - Adding prototype for Field_blob::char_length()
     @ sql/item.h
        - Adding new helper function char_to_byte_length_safe()
        - Using new function
     @ sql/protocol.cc
        Using new function char_to_byte_length_safe().

    modified:
      libmysqld/lib_sql.cc
      mysql-test/r/ctype_utf16.result
      mysql-test/r/ctype_utf32.result
      mysql-test/r/ctype_utf8.result
      mysql-test/r/ctype_utf8mb4.result
      mysql-test/t/ctype_utf16.test
      mysql-test/t/ctype_utf32.test
      mysql-test/t/ctype_utf8.test
      mysql-test/t/ctype_utf8mb4.test
      sql/field.cc
      sql/field.h
      sql/item.h
      sql/protocol.cc