read_clipboard() on master failing and not giving helpful message
The end user might need to know a better error. Strangely it worked for me once. I tried many times again after copying to clipboard the same thing and it didn't work.

```
In [34]: pd.read_clipboard()
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-34-475cedd2a1b1> in <module>()
----> 1 pd.read_clipboard()

/usr/local/lib/python2.7/dist-packages/pandas-0.11.1.dev_9713e45-py2.7-linux-x86_64.egg/pandas/io/clipboard.pyc in read_clipboard(**kwargs)
 12     from pandas.util.clipboard import clipboard_get
 13     text = clipboard_get()
---> 14     return read_table(StringIO(text), **kwargs)
 15 
 16 

NameError: global name 'read_table' is not defined
```
