snapshot: fix line order when skipping over empty deltas The code movement in 37957e07138c introduced an error. Since 8f83a953dddf, we discarded some revisions because they are identical to their delta base (and use that delta base instead). That logic is good, however, in 37957e07138c we mixed up the order of two line, adding the "new" revision to the set of already tested one, instead of the discarded one. So in practice, we were never investigating any revisions in a chain starting with an empty delta. Creating significantly worst delta chain (eg: Mercurial's manifest move goes from about 60MB up to about 80MB).

tests: stabilize change for handling not quoting non-empty-directory The change originated in cb1329738d64. I suspect the problem is with the combination of (re) and the '\' to '/' retry on Windows. I've no idea if py3 on Windows needs the quoting, since it can't even run `hg` with no arguments. (It's dying somewhere on the ctype declarations when win32.py is imported.)

hg: wrap the highest layer in the `hg` script possible in trace event This should help us have a better idea of what "interpreter startup costs" look like. This does omit the HGUNICODEPEDANTRY block and the LIBDIR dancing to set up sys.path, but the former is usually off and the latter is unavoidable and should be very fast. If we get worried about those cases we can consider open-coding the tracing logic here. Differential Revision: https://phab.mercurial-scm.org/D4346