Added a few more tests for the occurrence metric.
Added a few more tests for the occurrence metric.

faroit/mir_eval,mrgloom/mir_eval,bmcfee/mir_eval,urinieto/mir_eval,urinieto/mir_eval,faroit/mir_eval,craffel/mir_eval,craffel/mir_eval,mrgloom/mir_eval,rabitt/mir_eval,rabitt/mir_eval,bmcfee/mir_eval