rec_get_converted_size_new(): Rename to rec_get_converted_size_comp().
Add const qualifier to dtuple.  Remove the assertion
dict_table_is_comp(index->table), because this function will be invoked
when populating the temporary files in fast index creation.

rec_convert_dtuple_to_rec_new(): Rename to rec_convert_dtuple_to_rec_comp().
Add parameter "extra".

rec_init_offsets_comp_ordinary(): New function.  Used in rec_init_offsets().