tests/test-diff-newlines.t

sparse: treat paths as cwd-relative

This commit makes it so sparse treats passed paths as CWD-relative,
not repo-root-realive. This is a more intuitive behavior in my (and some
other FB people's) opinion.

This is breaking change however. My hope here is that since sparse is
experimental, it's ok to introduce BCs.

The reason (glob)s are needed in the test is this: in these two cases we
do not supply path together with slashes, but `os.path.join` adds them, which
means that under Windows they can be backslashes. To demonstrate this behavior,
one could remove the (glob)s and run `./run-tests.py test-sparse.t` from
MinGW's terminal on Windows.

  $ 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