The compress flag can be used to control compression, one of: (none),
"compress", "gzip", "bzip2", "xz", "lzop". Thus these calls can now
be used instead of tgz-in/tgz-out/txz-in/txz-out, and also support
more compression types.
Mark these APIs as once_had_no_optargs so that compatibility code is
generated.