Unescape quotes on parsing

Escaped quotes are unescaped at parse time.
See in `tests/text.po` line 90:

```
"the same title. If <a href=\"http://drupal.org/project/token\">token "
```

And in `tests/copy.po` line 105:

```
...the same title. If <a href="http://drupal.org/project/token">token...
```
