clonebundles: advertise clone bundles feature to clients Server operators that have enabled clone bundles probably want clients to use it. This patch introduces a feature that will insert a bundle2 "output" part that advertises the existence of the clone bundles feature to clients that aren't using it. The server uses the "cbattempted" argument to "getbundle" to determine whether a client supports clone bundles and to avoid sending the message to clients that failed the clone bundle for whatever reason.

exchange: advertise if a clone bundle was attempted The client now sends a "cbattempted" boolean flag to the "getbundle" wire protocol command to tell the server whether a clone bundle was attempted. The presence of this flag will enable the server to conditionally emit a bundle2 "output" part advertising the availability of clone bundles to compatible clients that don't have it enabled.

exchange: record that we attempted to fetch a clone bundle This is needed so a subsequent patch can conditionally add a bundle2 part to the "getbundle" wire protocol command depending on whether a clone bundle was attempted.

exchange: provide hint on how to disable clone bundles If a clone bundle persistently fails to apply, users need a way to disable it so they have a hope of the clone working. Change the hint for the abort scenario to advertise the config option to disable clone bundles.