[RFC] kbfiles: an extension to track binary files with less wasted bandwidth

[Andrew Pritchard]

Just a quick update on what's going on with what was once kbfiles:

I've changed it to use the SSH error stream and the HTTP content-type trick
along with moving the heads command to give non-kbfiles clients good error
messages.

I'm in the process of rebranding it to largefiles, as this seems to be the most
widely-accepted name.  Although this entails adding conversion logic to the
extension to handle the "old" repositories, that logic won't be present in the
final version submitted to the core repo.  Our extensions update themselves
automatically, so we can ship conversion logic for the intervening period and
be confident that any active repositories are converted by the time the next
version of Mercurial ships.

The Kiln-specific parts of the extension will be separated out into their own
meta-extension that we will ship with the other Kiln-specific extensions so as
to avoid polluting the core repository with legacy Kiln support.  Fortunately,
this is no more difficult than adding commands to Mercurial.

As always, the current state can be seen at
https://developers.kilnhg.com/Repo/Kiln/Group/Unstable