how to enable extension for hgweb?

[Alexis S. L. Carvalho]

Thus spake Christian Ebert:
> A note for anyone else needing this: it only works for me with
> /recent/ versions of Mercurial; I had 2f489b00f8eb on my public
> server and was wondering why it worked on my local machine and
> not on the other server. So one needs a more recent Mercurial
> than above for it to work -- 0.9.4 should be save.

I think 7c8f8b736365 (Jun 18) is the changeset that actually changed
things.  Before that one, extensions were never used with hgweb.

Alexis