Decide Moodle 3.1 requirements and push them to environment.xml (due date: 30/11/2015)

A) Standard testing: 0) To test exclusively in all supported stable branches. 1) Go to admin -> server -> environment 2) One "3.1 upwards" Moodle version should be available. 3) It shows the same requirements than a 3.0 version but with these differences: 3.1) The first check shows that Moodle 2.7 is required for installing 3.1. B) This release testing (requires database access): 1) Install Moodle 2.6.x+ (or older). 2) Upgrade codebase to master. 3) Start upgrade, both via web and cli, environment page/report must prevent upgrade to happen, detecting that 2.7 is required. 4) Edit your database and set change the "release" record in "config" table from "2.x.y..." (whatever you installed in step #1) to "2.7.y..." 5) Start upgrade again, also via web and cli, environment page/report now passes (because you've hacked the site badly) but, still, the process stops with message "You need to upgrade to 2.7.x or higher first!" under the core/system component. C) Run unit tests (mysql and mssql at very least). D) Install a 2.7.0 site with some real content (complex courses, users, repositories, availability...) and upgrade it to 3.1, also both via web and cli. Process should finish without problem.