Enhance spec task to convert specs before running them if needed
Remove test:transpec task
Enable matrix builds with RSpec versions
Split cached data for each RSpec version
Correct `expect` syntax restriction for non-test environment

It was unintentionally disabling other configuration options that are
added to the `config.mock_with` block by Transpec itself.
Fix a failing spec on RSpec 3
Exclude specs for RSpec 2 when run on RSpec 3
Run only `spec` task on builds except RSpec 2.14