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.

bundle: abort if the user request bundling of internal changesets See inline comments for details.

strip: do now include internal changeset in the strip backup See inline comment for details.

revset: add `_internal()` predicate This predicate help core code to select internal changeset (in the internal phase).

strip: drop the assert about bundled revision This is working well, so no need for extract computation. See the previous changeset for the rationnal of still have these assert around for a short interval.

strip: explicitly compute the boundary of the backup bundle We want to make change to the set of backed up revision in a future changeset, we start with a change of the computation without any changes in the semantic to clarify later changeset. The could of costly assert are here to testify that the result is still correct. They will be removed in the next changesets, but I wanted them in this changeset to help in case someone bisect a regression to this changeset in the future.