util: drop write_content_size=True This is now the default in python-zstandard 0.9. While we're here, also add a comment about the ability to drop frame magic to save space. Differential Revision: https://phab.mercurial-scm.org/D3199

zstandard: vendor python-zstandard 0.9.0 This was just released. It features a number of goodies. More info at https://gregoryszorc.com/blog/2018/04/09/release-of-python-zstandard-0.9/. The clang-format ignore list was updated to reflect the new source of files. The project contains a vendored copy of zstandard 1.3.4. The old version was 1.1.3. One of the changes between those versions is that zstandard is now dual licensed BSD + GPLv2 and the patent rights grant has been removed. Good riddance. The API should be backwards compatible. So no changes in core should be needed. However, there were a number of changes in the library that we'll want to adapt to. Those will be addressed in subsequent commits. Differential Revision: https://phab.mercurial-scm.org/D3198

revlog: reset _nodepos after strip When using the pure revlog parser, _nodepos is used to keep track of the position during index scanning in the non-cached cache. If it is out of bounds, BaseIndexObject._fix_index will assert. Since strip can actually remove the position scanned last, make sure to reset it. Add an assertion in the place where the invariance is clearer. Differential Revision: https://phab.mercurial-scm.org/D3188