dirstate-v2: correct documented return values of `pack_dirstate`

dirstate-v2: fix typos in docstrings

dirstate-v2: update constant that wasn't kept in sync Despite the best efforts of the comment, this constant wasn't kept in sync when the flags were being rewritten. The fact that this doesn't actually break anything in the Rust implementation too much (which does use directories) relies on the fact that all nodes can have children and that dirstate traversal is not based on that flag, but for metadata in optimizations. However the bug could become more serious should we start encoding stronger guarantees using a combination of flags including this one.

lfs: avoid closing connections when the worker doesn't fork Probably not much more than an minor optimization, but could be useful in the case of `hg verify` where missing blobs are fetched one at a time.

lfs: fix blob corruption when tranferring with workers on posix The problem seems to be that the connection used to request the location of the blobs is sitting in the connection pool, and then when workers are forked, they all see and attempt to use the same connection. This garbles everything. I have no clue how this ever worked reliably (but it seems to, even on Linux, with SCM Manager 1.58). See previous discussion when worker support was added[1]. It shouldn't be a problem on Windows, since the workers are just threads in the same process, and can see which connections are marked available and which are in use. (The fact that `mercurial.keepalive.ConnectionManager.set_ready()` doesn't acquire a lock does give me some pause though.) [1] https://phab.mercurial-scm.org/D1568#31621

keepalive: add `__repr__()` to the HTTPConnection class to ease debugging By default, this just printed the class name and memory address. By displaying the address and ports on both sides of the socket, it makes it easier to figure out what's in the ConnectionManager, and correlate with WireShark traces. It looks like the two connections mentioned in the previous commit come about because the LFS POST request to access the blobs opens connection 1, and gets a 401. Then for some reason, the follow up with credentials opens a new socket, instead of using the existing one in the pool. I have no clue why. This can be seen with something like this in the blobstore: ``` for h in self.urlopener.handlers: if hasattr(h, "close_all"): print('open connections on %s in pid %d' % (type(h), os.getpid())) for host, conns in h._cm.get_all().items(): for c in conns: print('connection: %r' % c) ```

keepalive: ensure `close_all()` actually closes all cached connections While debugging why LFS blob downloads are getting corrupted with workers, I noticed that prior to spinning up the workers, the ConnectionManager has 2 connections to the server and calling `KeepAliveHandler.close_all()` left one behind. The reason is the value component of `self._cm.get_all().items()` is a list, and `self._cm.remove()` modifies said list while the caller is iterating over it. Now `get_all()` is a deep copy of both the dict and lists in all cases.

tests: remove non-python3 line matching and tests block We don't support Python2 anymore