Supress potential E_NOTICES about integer overflows due to unusually high/low scores.

Fixes https://github.com/elasticsearch/elasticsearch-php/issues/145

This is solved by turning of `E_NOTICE`s momentarily within the method call. The `error_reporting` value is reverted back before exiting the method call.
Would you mind changing this to:

```php
isset(self::$messages[$code]) !== true
```

Just because the rest of the library already uses that formatting :)