page_zip_copy(), page_zip_compress_write_log(): Add parameter 'index'.

page_zip_parse_write_header(): Check for !page_zip only if page != NULL.

page_zip_compress_write_log(), page_zip_parse_compress(): Omit some
fields in the page header.  Omit the unused bytes between the modification
log and the page trailer.

parse_or_apply_log_rec_body(): Remove a bogus debug assertion.