rec_get_converted_size_comp(), rec_convert_dtuple_to_rec_comp(),
rec_convert_dtuple_to_rec_new(), rec_convert_dtuple_to_rec(): Add a
const qualifier to dict_index_t*.

row_search_on_row_ref(): Add const qualifiers to the dict_table_t*
and dtuple_t* parameters.  Note that pcur is an "out" parameter
and mtr is "in/out".