Add Eval.AuthoritativeMode option

Adds an `Eval.AuthoritativeMode` option that causes the `eval`, `create_function`, `preg_replace` with eval, and `hphp_set_property` (in reflection) error messages to be thrown without requiring the set up that RepoAuthoritative would normally require.

This should make it easier to find cases where this might happen during development, especially if you are using third-party code that uses these features without you realising it.