remote helpers: best practices for using the "refspec" capability

> | error: Ref refs/remotes/origin/master is at d94a46270250454f1fc6c1fb47abfde31a2196c9 but expected dfb79bbc658333d5c9b0427b71f6b1bc48629949
> | From mediawiki::http://localhost/mediawiki
> |  ! dfb79bb...c57c15b master     -> origin/master  (unable to update local ref)
> | error: Could not fetch origin
>
> which means that the transport machinery thought the helper was going
> to be fetching directly to "master".  I suspect you will want a
> 'refspec' capability like
>
>	refspec refs/heads/*:refs/mediawiki/${remotename}/*
>
> to fix this.
>
> Cc-ing Daniel who invented v1.7.0-rc0~62^2~19 (Allow helper to map
> private ref names into normal names, 2009-11-18).  What namespace
> should a helper use when asked to fetch to FETCH_HEAD without a remote
> name, like
>
>	git fetch mediawiki::testwiki
>
> ?