ImportError with pandas 0.20.0 and 0.20.1
#### Code Sample, a copy-pastable example if possible

With versions 0.20.0 and 0.20.1, I get the following error:
```python
import pandas
```
```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/smiel/.venvs/foo/local/lib/python2.7/site-packages/pandas/__init__.py", line 58, in <module>
    from pandas.io.api import *
  File "/home/smiel/.venvs/foo/local/lib/python2.7/site-packages/pandas/io/api.py", line 8, in <module>
    from pandas.io.clipboard.clipboard import read_clipboard
  File "/home/smiel/.venvs/foo/local/lib/python2.7/site-packages/pandas/io/clipboard/__init__.py", line 103, in <module>
    copy, paste = determine_clipboard()
  File "/home/smiel/.venvs/foo/local/lib/python2.7/site-packages/pandas/io/clipboard/__init__.py", line 76, in determine_clipboard
    return init_qt_clipboard()
  File "/home/smiel/.venvs/foo/local/lib/python2.7/site-packages/pandas/io/clipboard/clipboards.py", line 49, in init_qt_clipboard
    from PyQt4.QtGui import QApplication
ImportError: No module named sip
```
This does not occur with 0.19.2

Here are the other packages installed in my virtualenv
```
$ pip freeze
appdirs==1.4.3
numpy==1.12.1
packaging==16.8
pandas==0.20.1
pyparsing==2.2.0
python-dateutil==2.6.0
pytz==2017.2
PyYAML==3.12
six==1.10.0
```

#### Problem description

It would be nice if pandas was pip installable. As it stands, the new versions are not (for me).

#### Expected Output

No error when importing pandas.

#### Output of ``pd.show_versions()``

I can't get that info without being able to import pandas.

