JAGS has been updated to version 4.1.0. Following the last update (https://bugs.gentoo.org/show_bug.cgi?id=562644), I have tried to complete a proper pull request in github (https://github.com/gentoo/gentoo/pull/699). I hope this time will be more useful that my last try. Thank you.
commit b1376251f4604303695ee2c6949d825bceb82b71 Author: Xavier Fernández i Marín <xavier.fim@gmail.com> Date: Fri Oct 30 10:05:15 2015 +0100 sci-mathematics/jags: version bump