Mixed case bundle config variables

This commit correct an issue where you couldn't define config variables with uppercase letters in them.  The variables would be returned as `null` when you attempted to retrieve them.

For example in a bundle named "test"

If you had a config file `config/test.php`:
```php
return array("sampleOne" => "this is sample one", "sampleTwo" => "this is sample two");
```

`var_dump(Config::get('test::test.sampleOne')));` will return `null`.

However `var_dump(Config::get('test::test.sampleone')));` will give you the correct value of "this is a sample one".

Passes the core unit tests.

This should also close issue #1638 which describes the identical issue.