bundle2: support for bundling and unbundling payload
We add the ability to bundle and unbundle a payload in parts. The payload is the
actual binary data of the part. It is used to convey all the applicative data.
For now we stick to very simple implementation with all the data fit in single
chunk. This open the door to some bundle2 testing usage. This will be improved before
bundle2 get used for real. We need to be able to stream the payload in multiple
part to exchange any changegroup efficiently. This simple version will do for
now.
Bundling and unbundling are done in the same changeset because the test for
parts is less modular. However, the result is not too complex.
When Mercurial accepts more than one revision, they may be specified
individually, or provided as a topologically continuous range,
separated by the ":" character.
The syntax of range notation is [BEGIN]:[END], where BEGIN and END are
revision identifiers. Both BEGIN and END are optional. If BEGIN is not
specified, it defaults to revision number 0. If END is not specified,
it defaults to the tip. The range ":" thus means "all revisions".
If BEGIN is greater than END, revisions are treated in reverse order.
A range acts as a closed interval. This means that a range of 3:5
gives 3, 4 and 5. Similarly, a range of 9:6 gives 9, 8, 7, and 6.