This is going to warn every time `any_instance` is used even if they aren't using a block implementation.  Really, the warning is only needed if they use `any_instance` _and_ a block implementation.  We should find a better way to do this so that it only warns when needed; otherwise it'll be excessively noisy and annoying to users.  What about this?

if RSpec::Mocks.configuration.should_warn_about_any_instance_blocks?
  # default value; the user hasn't set it...
  me.warn_about_yielding_receiver_to_implementation_block = true
elsif RSpec::Mocks.configuration.yield_receiver_to_any_instance_implementation_blocks?
  me.and_yield_receiver_to_implementation
end
```

Basically, this would tell the message expectation to print the warning if/when the implementation block is set.  Then you can update `inner_implementation_action=` so that it prints a warning when called if the flag is set.