tests/test-diff-newlines.t

loggingutil: add basic logger backends

These classes will be used in command server. They are similar to
the blackboxlogger, but it can't be factored out since the blackbox is so
tightly coupled with a repo object.

  $ hg init

  $ "$PYTHON" -c 'open("a", "wb").write(b"confuse str.splitlines\nembedded\rnewline\n")'
  $ hg ci -Ama -d '1 0'
  adding a

  $ echo clean diff >> a
  $ hg ci -mb -d '2 0'

  $ hg diff -r0 -r1
  diff -r 107ba6f817b5 -r 310ce7989cdc a
  --- a/a	Thu Jan 01 00:00:01 1970 +0000
  +++ b/a	Thu Jan 01 00:00:02 1970 +0000
  @@ -1,2 +1,3 @@
   confuse str.splitlines
   embedded\r (no-eol) (esc)
  newline
  +clean diff