thirdparty: vendor attrs The attrs package allows defining namedtuple-like classes with no weird behavior and no runtime performance cost. This patch vendors in attrs 17.2.0. # no-check-commit Differential Revision: https://phab.mercurial-scm.org/D867

python3: don't byte mangle third-party packages Third-party packages are already expected to be dual-version clean. Differential Revision: https://phab.mercurial-scm.org/D871

tests: disable lints on mercurial/thirdparty In the next patch, this directory will be used to vendor in some third-party code. Differential Revision: https://phab.mercurial-scm.org/D866