Building docs SyntaxError
I followed [this](http://pandas.pydata.org/developers.html#contributing-to-the-documentation) advice but on `python make.py html` I get

```
Running Sphinx v1.2b3
Exception occurred while building, starting debugger:
Traceback (most recent call last):
  File "/usr/local/lib/python3.3/site-packages/sphinx/cmdline.py", line 245, in main
    warningiserror, tags, verbosity, parallel)
  File "/usr/local/lib/python3.3/site-packages/sphinx/application.py", line 119, in __init__
    self.setup_extension(extension)
  File "/usr/local/lib/python3.3/site-packages/sphinx/application.py", line 283, in setup_extension
    mod = __import__(extension, None, None, ['setup'])
  File "/Users/user/Optional/pandas/doc/sphinxext/numpydoc.py", line 40
    title_re = re.compile(ur'^\s*[#*=]{4,}\n[a-z0-9 -]+\n[#*=]{4,}\s*',
                                                                     ^
SyntaxError: invalid syntax
> /usr/local/lib/python3.3/site-packages/sphinx/application.py(283)setup_extension()
-> mod = __import__(extension, None, None, ['setup'])
(Pdb) 
```

I looked into doc/sphinxtest/numpydoc.py and noticed the `u''` strings in the re.\* functions. This incompatibility is not documented. https://github.com/pydata/pandas/commit/ff52cbb334f8b9c58b215efdc44752246ecc33ad says something about "py3 compat", but I am not sure if the "revert" refers to py3 compat or just to "docs".
