JAGS has been updated to version 4.2.0. I have completed a pull request at https://github.com/gentoo/gentoo/pull/956. Thank you.
commit 392357d2153784f4a9e9111be19c69f30d7ebbbb Author: Xavier Fernández i Marín <xavier.fim@gmail.com> Date: Tue Mar 1 16:46:25 2016 +0100 sci-mathematics/jags: version bump to 4.2.0