Fail build if warnings are emitted.
1.8.7's parser dislikes block arg defaults.
Direct RSpec warnings to stdout in our tests.

This is necessary so that only ruby warnings go to
stderr, so that we can fail the build for introducing
ruby warnings.
Work around JRuby error.

TypeError: $stderr must have write method, RSpec::StdErrSplitter given
Merge pull request #1118 from rspec/fail-build-for-ruby-warnings

Fail build if warnings are emitted.