report .netrc parse errors

A bad netrc file can cause weird messages, as seen in #2543.

```
* git lfs pre-push:
    Git pre-push hook implementation.
* git lfs smudge:
    Git smudge filter that converts pointer in blobs to the actual content.
line 1: keyword expected; got ine
```

It should be wrapped with a `netrc parse error:` prefix.