tests/test-issue4074.t

tests: force `dumbhttp.py` to write its log file with '\n' on Windows

This wasn't causing obvious test failures, but it's the same fix as dbd2d56224d1
for `dummysmtpd.py`, and there's no sense in leaving this problem lying around.
(And upon further review, it might have been causing some non-obviously related
failures- see the next commit.)

#require no-pure

A script to generate nasty diff worst-case scenarios:

  $ cat > s.py <<EOF
  > import random
  > for x in range(100000):
  >     print
  >     if random.randint(0, 100) >= 50:
  >         x += 1
  >     print(hex(x))
  > EOF

  $ hg init a
  $ cd a

Check in a big file:

  $ "$PYTHON" ../s.py > a
  $ hg ci -qAm0

Modify it:

  $ "$PYTHON" ../s.py > a

Time a check-in, should never take more than 10 seconds user time:

  $ hg ci --time -m1 --config worker.enabled=no
  time: real .* secs .user [0-9][.].* sys .* (re)