Failing interpolation test
```
$ nosetests pandas/tests/test_generic.py:TestSeries.test_interp_quad
F
======================================================================
FAIL: test_interp_quad (pandas.tests.test_generic.TestSeries)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/phillip/Documents/code/py/pandas/pandas/tests/test_generic.py", line 339, in test_interp_quad
    assert_series_equal(result, expected)
  File "/home/phillip/Documents/code/py/pandas/pandas/util/testing.py", line 452, in assert_series_equal
    assert_attr_equal('dtype', left, right)
  File "/home/phillip/Documents/code/py/pandas/pandas/util/testing.py", line 369, in assert_attr_equal
    assert_equal(left_attr,right_attr,"attr is not equal [{0}]" .format(attr))
  File "/home/phillip/Documents/code/py/pandas/pandas/util/testing.py", line 354, in assert_equal
    assert a == b, "%s: %r != %r" % (msg.format(a,b), a, b)
AssertionError: attr is not equal [dtype]: dtype('int64') != dtype('float64')

----------------------------------------------------------------------
Ran 1 test in 0.041s

FAILED (failures=1)
```
