don't use text mode in mkstemp

causes double-encoding of newlines,
preventing newline arg from having desired effect.

IPython/utils/tests/test_io.py

@@ -175,4 +175,41 @@ def test_atomic_writing():
                 f.write(u'written from symlink')
             
             with stdlib_io.open(f1, 'r') as f:
-                nt.assert_equal(f.read(), u'written from symlink')
+                nt.assert_equal(f.read(), u'written from symlink')
+
+def test_atomic_writing_newlines():
+    with TemporaryDirectory() as td:
+        path = os.path.join(td, 'testfile')
+        
+        lf = u'a\nb\nc\n'
+        plat = lf.replace(u'\n', os.linesep)
+        crlf = lf.replace(u'\n', u'\r\n')
+        
+        # test default
+        with stdlib_io.open(path, 'w') as f:
+            f.write(lf)
+        with stdlib_io.open(path, 'r', newline='') as f:
+            read = f.read()
+        nt.assert_equal(read, plat)
+        
+        # test newline=LF
+        with stdlib_io.open(path, 'w', newline='\n') as f:
+            f.write(lf)
+        with stdlib_io.open(path, 'r', newline='') as f:
+            read = f.read()
+        nt.assert_equal(read, lf)
+        
+        # test newline=CRLF
+        with atomic_writing(path, newline='\r\n') as f:
+            f.write(lf)
+        with stdlib_io.open(path, 'r', newline='') as f:
+            read = f.read()
+        nt.assert_equal(read, crlf)
+        
+        # test newline=no convert
+        text = u'crlf\r\ncr\rlf\n'
+        with atomic_writing(path, newline='') as f:
+            f.write(text)
+        with stdlib_io.open(path, 'r', newline='') as f:
+            read = f.read()
+        nt.assert_equal(read, text)