tests/test-diff-newlines.t

chg: let hgc_open support long path

"sizeof(sun_path)" is too small. Use the chdir trick to support long socket
path, like "mercurial.util.bindunixsocket".

It's useful for cases where TMPDIR is long. Modern OS X rewrites TMPDIR to a
long value. And we probably want to use XDG_RUNTIME_DIR [2] for Linux.

The approach is a bit different from the previous plan, where we will have
hgc_openat and pass cmdserveropts.sockdirfd to it. That's because the
current change is easier: chg has to pass a full path to "hg" as the
"--address" parameter. There is no "--address-basename" or "--address-dirfd"
flags. The next patch will remove "sockdirfd".

Note: It'd be nice if we can use a native "connectat" implementation.
However, that's not available everywhere. Some platform (namely FreeBSD)
does support it, but the implementation has bugs so it cannot be used [2].

[1]: https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
[2]: https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-April/082892.html

  $ hg init

  $ $PYTHON -c 'file("a", "wb").write("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