TravisCI: use "travis_retry" for network dependent cmds.
travis_retry: http://blog.travis-ci.com/2013-05-20-network-timeouts-build-retries/
TravisCI: enabled fast_finish and re-arranged build matrix
fast_finish: http://docs.travis-ci.com/user/build-configuration/#Fast-finishing
TravisCI: Implement retry in RunTravis.hx.
Seems like travis_retry cannot be called by `Sys.command()`...?