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.