Include file path in error message

Currently, if there's a syntax error in the package.json, browserify quits with a fairly cryptic message:

```cpp
> browserify index.js
SyntaxError: Unexpected token }
```

After some time I figured out this wasn't a syntax error in my source code, rather it was in the package.json and the error was coming out of `node-browser-resolve`. Would be nice if `node-browser-resolve` exposed the file name causing the parse error if it comes across one.