Squat on less of the user's method namespace.

RSpec::Mocks::ExampleMethods is mixed into a context
where users freely define their own methods.  As such,
it's best to not define private helper methods as the
user may inadvertently overwrite them. These methods
were all stateless, anyway, so they work equally well
as class methods and this creates less surface area
for override problems.
Merge pull request #459 from rspec/less-namespace-squatting

Squat on less of the user's method namespace.