fix($parse): allow for new lines in expr when promise unwrapping is on

Previously, when unwrapping promises was set to `true`, (via `$parseProvider.unwrapPromises(true);`)
an error would occur if a parsed expression had a new line in it.

This was because when generating the `evaledFnGetter` [code](https://github.com/angular/angular.js/blob/d434eabec3955f8d56c859c93befe711bfa1de27/src/ng/parse.js#L1020),
a new line in an parsed expression would create a new line in a JS string in that code, which is illegal. 

That is:
```js
pw("A+
B")
```

Plunk with 1.2.0-rc.3: http://plnkr.co/edit/QHJHkQOViLYQYNveMnVL?p=preview
Plunk with this PR: http://plnkr.co/edit/sI1e4vCSw4HBZnjitojG?p=preview