travis-ci/travis-core — pull request #301 by BanzaiMan (2013-12-06 13:35:16+00:00)
Title: Expand build matrix only on relevant factors

Build matrices should be constructed in such a way that
only relevant ones are built; for example, if the language
is 'python', it does not make sense to expand on 'rvm' or 'gemfile'.

These choices are hardcoded in `Build::EXPANSION_KEYS_LANGUAGE`.
We always expand on the keys `Build::EXPANSION_KEYS_UNIVERSAL`.

Also, eradicate use of `Build.expand_matrix_config`.