py3: fix test-diff-newlines.t to be compatible with py3

contrib/python3-whitelist

@@ -1,34 +1,35 b''
 test-ancestor.py
 test-backwards-remove.t
 test-branch-tag-confict.t
 test-casecollision.t
 test-check-commit.t
 test-check-execute.t
 test-check-pyflakes.t
 test-check-pylint.t
 test-check-shbang.t
 test-contrib-check-code.t
 test-contrib-check-commit.t
 test-ctxmanager.py
 test-diff-issue2761.t
+test-diff-newlines.t
 test-diff-reverse.t
 test-diff-subdir.t
 test-dirstate-nonnormalset.t
 test-doctest.py
 test-empty-dir.t
 test-excessive-merge.t
 test-issue1089.t
 test-issue1993.t
 test-issue842.t
 test-locate.t
 test-lrucachedict.py
 test-manifest.py
 test-merge-default.t
 test-merge-subrepos.t
 test-merge2.t
 test-merge5.t
 test-revlog-packentry.t
 test-run-tests.py
 test-unified-test.t
 test-update-reverse.t
 test-xdg.t

tests/test-diff-newlines.t

@@ -1,19 +1,19 b''
   $ hg init
 
-  $ $PYTHON -c 'file("a", "wb").write("confuse str.splitlines\nembedded\rnewline\n")'
+  $ $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