Fix '%%cellm?' case, make tests more stringent to catch error.

IPython/core/inputsplitter.py

@@ -840,7 +840,7 b' class IPythonInputSplitter(InputSplitter):'
         # If the entire input block is a cell magic, return after handling it
         # as the rest of the transformation logic should be skipped.
         if lines.startswith('%%') and not \
-          (len(lines.splitlines()) == 1 and lines.endswith('?')):
+          (len(lines.splitlines()) == 1 and lines.strip().endswith('?')):
             return self._handle_cell_magic(lines)
 
         # In line mode, a cell magic can arrive in separate pieces

IPython/core/tests/test_inputsplitter.py

@@ -624,7 +624,7 b' class IPythonInputTestCase(InputSplitterTestCase):'
                 if raw.startswith(' '):
                     continue
 
-                isp.push(raw)
+                isp.push(raw+'\n')
                 out, out_raw = isp.source_raw_reset()
                 self.assertEqual(out.rstrip(), out_t,
                         tt.pair_fail_msg.format("inputsplitter",raw, out_t, out))