Update yum packages.

* Remove sqlite and QT dependency.
* Remove implicit dependencies; let yum find and install them.
* Install pyOpenSSL for safety.
* Update bitcoin release to 1.6.
* Do not install bitcoin release if already present. Fixes #967.
* Install ZeroMQ version 3.
* Group dependencies in multiple installations.
Setup a virtualenv on Gentoo.

* Fixes #1132.