NameError: global name 'PythonToVimStr' is not defined

I'm getting this stack flashed at me each time I open vim on the latest master.

```python
Error detected while processing /home/steve/.vim/bundle/jedi-vim/autoload/jedi.vim:
line  284:
Traceback (most recent call last):
  File "<string>", line 15, in <module>
  File "/home/steve/.vim/bundle/jedi-vim/jedi_vim.py", line 62, in <module>
    echo_highlight('Please update your Jedi version, it is to old.')
  File "/home/steve/.vim/bundle/jedi-vim/jedi_vim.py", line 58, in echo_highlight
    vim_command('echohl WarningMsg | echom "%s" | echohl None' % msg)
  File "/home/steve/.vim/bundle/jedi-vim/jedi_vim.py", line 54, in vim_command
    _catch_exception(string, 0)
  File "/home/steve/.vim/bundle/jedi-vim/jedi_vim.py", line 43, in _catch_exception
    result = vim.eval(e % (repr(PythonToVimStr(string, 'UTF-8')), is_eval))
NameError: global name 'PythonToVimStr' is not defined
```

I haven't actually tested this, but it seems pretty obvious what the fix is - just looks like a simple reference before definition problem.