Fix split_user_input to correctly handle %% escape for cell magics.

IPython/core/splitinput.py

@@ -44,7 +44,7 b' from IPython.utils.encoding import get_stream_enc'
 line_split = re.compile("""
              ^(\s*)               # any leading space
              ([,;/%]|!!?|\?\??)?  # escape character or characters
-             \s*(%?[\w\.\*]*)     # function/method, possibly with leading %
+             \s*(%{0,2}[\w\.\*]*)     # function/method, possibly with leading %
                                   # to correctly treat things like '?%magic'
              (.*?$|$)             # rest of line
              """, re.VERBOSE)

IPython/core/tests/test_splitinput.py

@@ -20,7 +20,10 b' tests = ['
     ('  ;ls', ('  ', ';', 'ls', '')),
     ('f.g(x)',  ('', '', 'f.g', '(x)')),
     ('f.g (x)', ('', '', 'f.g', '(x)')),
-    ('?%hist', ('', '?', '%hist', '')),
+    ('?%hist1', ('', '?', '%hist1', '')),
+    ('?%%hist2', ('', '?', '%%hist2', '')),
+    ('??%hist3', ('', '??', '%hist3', '')),
+    ('??%%hist4', ('', '??', '%%hist4', '')),
     ('?x*', ('', '?', 'x*', '')),
     ]
 if py3compat.PY3: