Is there a Mercurial extension like svn propset?

I need to attach custom metadata to my source files that at tracked via Mercurial. The svn properties commands are exactly what I need.

Is there a mercurial extension that provides commands similar to propset, propget, propdel, etc?

If there isn't an extension, why not?
Is there an alternative/better approach for custom metadata when using Mercurial?
Is custom metadata not useful to anyone else?
Is the extension dearly desired but just not written yet?

extra info: If it helps. The metadata I'm tracking is whether each file has been codereviewed, unittested, qa'd, etc. This data needs to be traceable and merges between branches/clones aren't fine grained enough.