Add a new regression test and fix for it

IPython/core/inputtransformer2.py

@@ -636,7 +636,8 b' class TransformerManager:'
                 MemoryError, SyntaxWarning):
             return 'invalid', None
         else:
-            if len(lines) > 1 and not lines[-1].strip().endswith(':'):
+            if len(lines) > 1 and not lines[-1].strip().endswith(':') \
+                              and not lines[-2][:-1].endswith('\\'):
                 return 'incomplete', find_last_indent(lines)
         return 'complete', None
 

IPython/core/tests/test_inputtransformer2.py

@@ -206,6 +206,7 b' def test_check_complete():'
     nt.assert_equal(cc("a = '''\n   hi"), ('incomplete', 3))
     nt.assert_equal(cc("def a():\n x=1\n global x"), ('invalid', None))
     nt.assert_equal(cc("a \\ "), ('invalid', None))  # Nothing allowed after backslash
+    nt.assert_equal(cc("1\\\n+2"), ('complete', None))
 
     # no need to loop on all the letters/numbers.
     short = '12abAB'+string.printable[62:]