Use faster Travis CI Build Process

Explanation:
http://blog.travis-ci.com/2014-12-17-faster-builds-with-container-based-infrastructure/
fix environment variables
use same swig version as in Ubuntu 14.04
remove use-mirrors option (deprecated)
Merge pull request #995 from PyBossa/faster-travis-ci

Faster travis ci
Merge branch 'master' into issue-landscape
Fix number of arguments on overriden method.
Fix number of arguments in overridden method.
Fix overridden method number of args.
Fix redifinning built-in 'id'
Disable temporary cyclic imports.