PHP Warning fix + extraParameters from config

1. Fixed PHP Warning: If we're using Resque - we are almost guaranteed to load it ourselves in order to configure it. Since `class_exists()` tries to autoload by default, this raises a PHP Warning every time an exception is handled. Setting `$autoload=false` on the parameter list makes sure it only tests for already existing Resque, not attempt to include it as well.
2. You can now include 'extraParameters' in your configuration as well and it will be sent to Airbrake's "parameters" field (used to have to be hard coded?)
This implies that you've already loading the Resque class in some way. This could be problematic to people who rely on the autoloader to locate the the Resque class.

Can you provide more context on the warning that this causes, so we can find a solution that wouldn't possibly break this functionality for some people?