BUG: Failing eval tests on OS X
These two tests fail (note the warning that it generates, happens in one other place but the test passes).

```
pandas.computation.tests.test_eval.TestAlignment.test_basic_series_frame_alignment('numexpr', 'python') ... /Users/jtratner/scratch/pandas/pandas/core/index.py:900: RuntimeWarning: tp_compare didn't return -1 or -2 for exception
  result.sort()
FAIL
pandas.computation.tests.test_eval.TestAlignment.test_basic_series_frame_alignment('numexpr', 'pandas') ... FAIL
```

Traceback:

```
FAIL: pandas.computation.tests.test_eval:TestAlignment.test_basic_series_frame_alignment('numexpr', 'python')
  /usr/local/bin/vim +872 pandas/computation/tests/test_eval.py  # check_basic_series_frame_alignment
    testit(r_idx_type, c_idx_type, index_name)
  /usr/local/bin/vim +867 pandas/computation/tests/test_eval.py  # testit
    assert_frame_equal(res, expected)
  /usr/local/bin/vim +312 pandas/util/testing.py  # assert_frame_equal
    assert_index_equal(left.columns, right.columns)
  /usr/local/bin/vim +192 pandas/util/testing.py  # assert_index_equal
    right.dtype))
AssertionError: [index] left [object Index([1, 2000-01-03 00:00:00, 2000-01-04 00:00:00, 2000-01-05 00:00:00, 
2, 4, 3, 0, 2000-01-06 00:00:00, 2000-01-07 00:00:00, 2000-01-10 00:00:00, 2000-01-11 00:00:00], dtype=object)], 
right [Index([2000-01-03 00:00:00, 2000-01-04 00:00:00, 2000-01-05 00:00:00, 2000-01-06 00:00:00, 
2000-01-07 00:00:00, 2000-01-10 00:00:00, 2000-01-11 00:00:00, 0, 1, 2, 3, 4], dtype=object) object]

FAIL: pandas.computation.tests.test_eval:TestAlignment.test_basic_series_frame_alignment('numexpr', 'pandas')
  /usr/local/bin/vim +872 pandas/computation/tests/test_eval.py  # check_basic_series_frame_alignment
    testit(r_idx_type, c_idx_type, index_name)
  /usr/local/bin/vim +867 pandas/computation/tests/test_eval.py  # testit
    assert_frame_equal(res, expected)
  /usr/local/bin/vim +312 pandas/util/testing.py  # assert_frame_equal
    assert_index_equal(left.columns, right.columns)
  /usr/local/bin/vim +192 pandas/util/testing.py  # assert_index_equal
    right.dtype))
AssertionError: [index] left [object Index([1, 2000-01-03 00:00:00, 2000-01-04 00:00:00, 2000-01-05 00:00:00, 
2, 4, 3, 0, 2000-01-06 00:00:00, 2000-01-07 00:00:00, 2000-01-10 00:00:00, 2000-01-11 00:00:00], dtype=object)], 
right [Index([2000-01-03 00:00:00, 2000-01-04 00:00:00, 2000-01-05 00:00:00, 2000-01-06 00:00:00, 
2000-01-07 00:00:00, 2000-01-10 00:00:00, 2000-01-11 00:00:00, 0, 1, 2, 3, 4], dtype=object) object]
```
