test_precise_conversion failure on 32bit boxes
```
======================================================================
FAIL: test_precise_conversion (pandas.io.tests.test_parsers.TestCParserLowMemory)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/buildd/pandas-0.15.0/debian/tmp/usr/lib/python2.7/dist-packages/pandas/io/tests/test_parsers.py", line 3204, in test_precise_conversion
    self.assertTrue(sum(precise_errors) <= sum(normal_errors))
AssertionError: False is not true
```
