Also, this message really only makes sense in the context of `rspec-core`.  Consider that rspec-mocks can be used with other frameworks (e.g. test-unit, minitest, shindo, cucumber, etc).  Getting a warning about `before(:all)` would be very confusing if you're not using rspec-core.

Instead, here's what I think we should do:

* Have a default warning message that says something like: "the use of doubles or partial doubles from rspec-mocks outside of the per-test lifecycle is not supported".  This message could make sense in any test framework.
* Provide a config option that rspec-core will use to inject an rspec-core specific message that mentions `before(:all)`.  This could completely override the default warning message or simply add some text to append to it (or to interpolate in the middle of it -- not sure what's best yet).