Create class doubles in our example so they have a full lifecycle.

...rather than creating them in a nested example, which resets
them before they get used.

This is necessary for rspec/rspec-mocks#718.
Merge pull request #1613 from rspec/address-class-double-lifecycle-violations

Create class doubles in our example so they have a full lifecycle.
Add a changelog entry for #1606
Fix color on Shared Example Group failure.

Now is white to separate it from the stack trace.