Pairinggroup does not allow to test for membership in specific group

[chrmatt]

Pairinggroup consists of four different groups: ZR, G1, G2, and GT. The methods ismember and ismemberList take an object and check whether it is in any of these groups. It should also be possible to check for membership in a specific group, e.g., G1. Such functionality is needed when verifying signatures, to ensure that elements are in the correct groups.