Edited Issue: Object fields should be quoted where appropriate [431]

E.g. consider an object like so:
```
o = {foo: 0, 'foo.bar': 1, 'foo bar': 2, 'foo=bar': 3};
```
This is a perfectly valid object, but its fields are not identifiers. Yet, when we display it in debugger windows like Locals, we do show them as (invalid) identifiers, i.e.:
```
foo
+- foo | 0
+- foo.bar | 1
+- foo bar | 2
+- foo=bar | 3
```
What we should do in this case is quote any such names, i.e.:
```
foo
+- foo | 0
+- 'foo.bar' | 1
+- 'foo bar' | 2
+- 'foo=bar' | 3
```