BLD: test_to_html_compat: AttributeError: 'NoneType' object has no attribute 'next_element'
Trying current master build on Debian sid with 

```
$> welp bs4
PATH       : /usr/lib/python2.7/dist-packages/bs4/__init__.pyc
SRC PATH   : /usr/share/pyshared/bs4/__init__.py
VERSION    : Not found
__version__: '4.2.0'
PACKAGE    : python-bs4
ii  python-bs4                                                  4.2.0-2                                    all          error-tolerant HTML parser for Python
python-bs4:
  Installed: 4.2.0-2
  Candidate: 4.2.0-2
  Version table:
 *** 4.2.0-2 0
        900 http://debian.lcs.mit.edu/debian/ jessie/main amd64 Packages
        600 http://debian.lcs.mit.edu/debian/ sid/main amd64 Packages
        100 /var/lib/dpkg/status
     4.1.0-1 0
        100 http://debian.lcs.mit.edu/debian/ wheezy/main amd64 Packages
```

test crashes

```
======================================================================
ERROR: test_to_html_compat (pandas.io.tests.test_html.TestReadHtmlBase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/yoh/deb/gits/pkg-exppsy/build-area/pandas-0.11.0+git43-g7b2eaa4/debian/tmp/usr/lib/python2.7/dist-packages/pandas/io/tests/test_html.py", line 88, in test_to_html_compat
    index_col=0)[0]
  File "/home/yoh/deb/gits/pkg-exppsy/build-area/pandas-0.11.0+git43-g7b2eaa4/debian/tmp/usr/lib/python2.7/dist-packages/pandas/io/tests/test_html.py", line 67, in run_read_html
    return read_html(*args, **kwargs)
  File "/home/yoh/deb/gits/pkg-exppsy/build-area/pandas-0.11.0+git43-g7b2eaa4/debian/tmp/usr/lib/python2.7/dist-packages/pandas/io/html.py", line 900, in read_html
    attrs)
  File "/home/yoh/deb/gits/pkg-exppsy/build-area/pandas-0.11.0+git43-g7b2eaa4/debian/tmp/usr/lib/python2.7/dist-packages/pandas/io/html.py", line 772, in _parse
    for table in tables]
  File "/home/yoh/deb/gits/pkg-exppsy/build-area/pandas-0.11.0+git43-g7b2eaa4/debian/tmp/usr/lib/python2.7/dist-packages/pandas/io/html.py", line 186, in <genexpr>
    return (self._build_table(table) for table in tables)
  File "/home/yoh/deb/gits/pkg-exppsy/build-area/pandas-0.11.0+git43-g7b2eaa4/debian/tmp/usr/lib/python2.7/dist-packages/pandas/io/html.py", line 345, in _build_table
    body = self._parse_raw_tbody(table)
  File "/home/yoh/deb/gits/pkg-exppsy/build-area/pandas-0.11.0+git43-g7b2eaa4/debian/tmp/usr/lib/python2.7/dist-packages/pandas/io/html.py", line 367, in _parse_raw_tbody
    res = self._parse_tr(tbody[0])
  File "/home/yoh/deb/gits/pkg-exppsy/build-area/pandas-0.11.0+git43-g7b2eaa4/debian/tmp/usr/lib/python2.7/dist-packages/pandas/io/html.py", line 399, in _parse_tr
    return element.find_all('tr')
  File "/usr/lib/python2.7/dist-packages/bs4/element.py", line 1167, in find_all
    return self._find_all(name, attrs, text, limit, generator, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bs4/element.py", line 485, in _find_all
    return [element for element in generator
  File "/usr/lib/python2.7/dist-packages/bs4/element.py", line 1185, in descendants
    current = current.next_element
AttributeError: 'NoneType' object has no attribute 'next_element'
```
