Fixup Rakefile deprecations
Created by: JonRowe
If RSpec is already loaded (it's common to do:
require 'rspec' # or 'rspec/core'
require 'rspec/core/rake_task'
in a Rakefile
), and we can safely use the built in deprecation support however otherwise it's become to complicated to load the deprecation file alone so we drop back to a simplier warn.
If we don't do this, the deprecated methods will blow up unless require 'rspec/core'
has been required, or we have to require most of rspec/core
due to the use of configuration
and the formatters.