tests/test-issue4074.t

py3: use stringutil.pprint() to print NoneType

Before this patch, when running test-debugcommands.t, we get a TypeError because
NoneType can't be converted into bytes. This patch uses stringutil.pprint() to
print the ui._colormode.

We are now close to getting test-debugcommands.t passing on Python 3.

Differential Revision: https://phab.mercurial-scm.org/D3831

#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
  time: real .* secs .user [0-9][.].* sys .* (re)