output impostor and genuine matches around the EER score threshold.

@jklontz This is the change to the visualization of matches talked about earlier.  Please review.
You can test it with the command:
`br -path MEDS-II/img/ -algorithm FaceRecognition -compare ~/openbr/data/MEDS/sigset/MEDS_frontal_target.xml ~/openbr/data/MEDS/sigset/MEDS_frontal_query.xml meds.mtx -eval meds.mtx meds.csv 10 -plot meds.csv meds.pdf`
Yep I'll change that