Switch from coveralls to our simplecov setup.
Fix ruby warning.
Fix our simplecov setup.

Simplecov was only reporting coverage for a handful
of rspec's files, and I realized why: simplecov can
only track coverage of files that are loaded _after_
it has been loaded. So, to get this to work properly,
we have to load simplecov before rspec-core. This
commit adds a wrapper script that does that.
Coverage is a bit lower on JRuby.
Merge pull request #1205 from rspec/use-simplecov-setup

Use simplecov setup