do not hide user provided TRAVIS_* env vars
always export TRAVIS_LANGUAGE
simplify env vars, use Ruby tainting for secure env vars
push replacing secure env var display value down to the generator
shellescape all builtin env var values
raise an exception if tainted output ends up in the compiled code
improve spec coverage for Env
Merge pull request #330 from travis-ci/sf-taint-env-vars

Taint env vars