extras: re-use Projection from jaraco.collections

extras: expose 'retained_extras' for extensions to extend

extras: extract function for projecting names from a gettable object

hgweb: add "children" into the JSON template for a changeset The children are shown in the HTML templates, so I don’t see a reason against including them in the JSON template as well.

branching: merge stable into default

help: fix formatting for http config section

branching: merge stable into default

fastexport: rework newline logic Newlines should only be added when otherwise the stream would look weird without them (on blobs), therefore they are the exception. Flip the logic so they are added, not skipped.

encoding: avoid quadratic time complexity when json-encoding non-UTF8 strings Apparently the code uses "+=" with a bytes object, which is linear-time, so the whole encoding is quadratic-time. This patch makes us use a bytearray object, instead, which has a(n amortized-)constant-time append operation. The encoding is still not particularly fast, but at least a 10MB file takes tens of seconds, not many hours to encode.

bundle: prevent implicite bundling of internal changeset Now that the two mains source of on-disk bundle are preventing the inclusion of internal changesets in their bundling. We can add a lower level check that would prevent any other leakage of internal-phase changesets. We keep the door open to some usage, like the temporary bundle using during strip for example.