largefiles: drop the unused lfcommands._addchangeset()

largefiles: use the convert extension for 'lfconvert --to-normal' The logic in the convert extension is more advanced, supporting extra features like converting revision IDs in 'extras' (e.g. 'amend_source'), supports updating hashes in commit messages, and outputs an SHA map file. Rather than try to duplicate all of that, just use the existing code. Even though the convert extension supports user supplied options like filemap, etc, those features aren't available on the lfconvert interface. Therefore, it is safe to use the filemap mechanism (in memory) to handle the standin -> file rename. The convert extension handles the destination locking for this path. There was a comment in test-lfconvert.t about the hash on rev 5 being different because it was doing a better job than "hg remove" + "hg merge" + "hg commit". It isn't clear to me what was happening or why, but now the hashes match the original repo exactly after a roundtrip, which seems like a good idea. If there really was something beneficial about the previous behavior, perhaps merge can be changed so that everyone benefits. Converting to a largefiles repo still uses the original (limited) lfconvert logic.

bundle2: add generic debug output regarding generated interruption If we are about to hide the detailed debug output, we need some generic debug message to replace it in a concise way.