Don't perform any caching when controller.perform_caching returns false

Fix #138
Provide instance_eval for tests in case it's missing

An issue with recent version of JRuby, see: https://travis-ci.org/rails/jbuilder/jobs/8699816
Allow CI failures for ruby-head

See: https://twitter.com/travisci/status/352451358563110915
Depend on released actionpack and railties v4.0.0 in tests
Dirty version or partial collection rendering
Allow rbx fail on CI

because https://travis-ci.org/rails/jbuilder/jobs/8701837
This shouldn't be commented
Merge branch 'master' of https://github.com/rails/jbuilder