Request discids for release lookups.

I wrote a CD ripping plugin for Picard (https://code.google.com/p/picard-cd-ripper/). For this to work I need to know the discids for a given release. When you press CD Lookup, you will get the discid of the CD in the drive but no reference to which medium on a release it belongs to. By pulling discids with the release lookup, I can compare the discid obtained from the CD Lookup dialog to the discids for each medium and rip the disc appropriately.