allowProtoMethods/Properties runtime options do not work for nested objects

For example, given the following input:

``` javascript
function TestClass() {}
TestClass.prototype.aMethod = function() {
return 'returnValue'
};
TestClass.prototype.nested = new TestClass()
const context = new TestClass()
```

the following,
``` javascript
const template = Handlebars.compile('{{nested.aMethod}}')
template(context, {allowProtoMethodsByDefault: true})
```
should yield `'returnValue'`. Instead, it yields `'undefined'`.

PR with failing test-cases submitted: #1859.

Start with the failing test cases in PR #1859 and trace how allowProtoMethodsByDefault is applied during nested property lookup. Done means compiling {{nested.aMethod}} with the shown TestClass context returns 'returnValue' when the runtime option is enabled.

Written by the indexing model from the issue text.