rust-status: collect traversed directories if required Some commands (`hg purge` notably) register the `traversedir` callback on their matcher to run said callback every time a directory is traversed. This is the first of three patches, further broadening Rust support for status. Unfortunately, there is no way around collecting a full `Vec` (or any other owned datastructure, like a radix tree) and pushing it back up the Python layer since keeping the Python callback in a closure would mean giving up multithreading because of the GIL, which is obviously unacceptable. Performance is still a lot better than the Python+C path. Running `hg clean/purge` on Netbeans' repo (100k files): ``` | No-op | 30% unknown -------------------------- Rust | 1.0s | 1.67s C | 2.0s | 2.87s ``` Differential Revision: https://phab.mercurial-scm.org/D8518

rust-status: don't dispatch unknown file when traversing if not listing unknowns This usually isn't a (functional) problem since we ignore the unknown files anyway, but when specifically using `hg purge`, unknown files were iterated over regardless of the option being true. This is both more correct and more efficient. Differential Revision: https://phab.mercurial-scm.org/D8517

status: update comment to reflect the more recent situation This is a gratuitous cleanup. Differential Revision: https://phab.mercurial-scm.org/D8516