fix bug 1035946 - urllib.unquote does not like ints, and backslash will

wreak havoc with the CSV->postgres import
```\``` is the escape sequence for Python:
https://docs.python.org/2/reference/lexical_analysis.html#string-literals

For example, it's used to represent things like linefeed (```\n```), but it can also be used to escape characters like ```'``` and ```"```:

```
>>> s = '"foo"=\'bar\''
```

So to encode a single ```\``` you must use ```\\```, otherwise you're escaping the ```'```:

```
>>> 'foo'.replace('\', '\\')
  File "<stdin>", line 1
    'foo'.replace('\', '\\')
                           ^
SyntaxError: unexpected character after line continuation character
```