Fix handling of repeated NEWLINE tokens

IPython/core/inputtransformer2.py

@@ -674,8 +674,8 b' class TransformerManager:'
         while tokens_by_line[-1] and tokens_by_line[-1][-1].type in newline_types:
             tokens_by_line[-1].pop()
 
-        if len(tokens_by_line) == 1 and not tokens_by_line[-1]:
-            return 'incomplete', 0
+        if not tokens_by_line[-1]:
+            return 'incomplete', find_last_indent(lines)
 
         if tokens_by_line[-1][-1].string == ':':
             # The last line starts a block (e.g. 'if foo:')

IPython/core/tests/test_inputtransformer2.py

@@ -265,6 +265,8 b' def test_check_complete():'
         for k in short:
             cc(c+k)
 
+    nt.assert_equal(cc("def f():\n  x=0\n  \\\n  "), ('incomplete', 2))
+
 def test_check_complete_II():
     """
     Test that multiple line strings are properly handled.