surt() breaks up query incorrectly if parameter value contains (%-escaped) "&"

```
>>> import surt
>>> url = ""http://exmaple.com/script?type=a+b+%26+c&grape=wine"
>>> surt.surt(url)
'com,exmaple)/script?+c&grape=wine&type=a+b+'
```
Desired output is `com,exmaple)/script?grape=wine&type=a+b+%26+c`

Problem is in `surt.GoogleURLCanonicalizer.minimalEscape`:
```
def minimalEscape(input):
return escapeOnce(unescapeRepeatedly(input))
```
This function turns query part of the url into `grape=wine&type=a+b+&+c`. It's clearly wrong to apply `unescapeRepeatedly` on entire query part.

I'd also question the usefulness of applying unquoting repeatedly in general. While there may be a cases where it's useful, it'd be more harmful for most of the cases.