bundle2: use chunkbuffer for exchange.getbundle We can use `util.chunkbuffer` instead.

bundle2: lazily generate the changegroup part in exchange.getbundle Now that we have lazy generation of parts, let's use it.

bundle2: support chunk iterator as part data When the `part.data` attribute is an iterator, we assume it is an iterator of chunks and use it. We use a chunkbuffer to yield chunks of 4096 bytes. The tests are updated to use this feature.

bundle2: extract a _payloadchunks method for part We are preparing streaming capability for part. So the generation of payload chunk will becomes more complex. We extract this part in its own function before any changes.

changegroup: move chunk extraction into a getchunks method of unbundle10 This code used to be in `writebundle` only. We needs to make it more broadly available for bundle2. The "changegroup" bundle2 part has to retrieve the binary content of changegroup stream. We moved the chunks retrieving code into the `unbundle10` object directly and the `writebundle` code is now using that. This split is useful for bundle2 purpose, we want to be able to easily stream changegroup content in a part. To keep thing simples, we kept compression out of the new methods. If it make more sense in the future, compression may get included in this function too.

bundle2: use reply part to return result of addchangegroup We now have an official way to return the result of addchangegroup. The tests are updated to check that the return bundle is properly created. It will be used when push is bundle2 enabled.

bundle2: produce a bundle2 reply We do not know yet what kind of data future features and extensions will need to exchange. To handle that, bundle2 allows to send arbitrary content to the server. As a consequence, we need to be able to reply arbitrary content to the client. And, we can use bundle2 to transmit those arbitrary data. When a client will push a bundle2 to the server, the server will reply with a bundle2 itself. This changeset installs the first stone of this logic and test it.

bundle2: add reply awareness to unbundlerecords We need an efficient way to handle bundle replies. The unbundle records class is extended to carry such data.

bundle2: add an integer id to part For sending response to a pushed bundle, we need to link reply parts to request part. We introduce a part id for this purpose. This is a 32 bit unique integer stored in the header.

largefiles: don't prompt when one side of merge was changed but didn't change This can happen after backout or grafts or criss cross merges. We already do the same (but slightly different) thing in manifestmerge and filemerge.

color: fallback and test label as an effect With this changeset, we can now send a color name directly to the label function, e.g. $ hg log -r . -T "{label('red', node|short)}\n"

color: extract method for determining a valid effect This patch is just setup work so that we can reduce code duplication and have one place to define a valid effect.

revlog: use context ancestor instead of changelog ancestor We want to move in this direction.

copies: guard debug section with ui.debugflag