The "--test-recursive" does not necessarily do what people think

[zimmski]

If we do "go-mutesting --test-recursive some/package/..." we will go through every Go file and mutate it. The "--test-recursive" option here would maybe indicate to the user that we will run ALL test cases of "some/package". However, we only run the test cases of the package the current Go file belongs to plus all subpackages. This seems confusing and we should give a better usability for this case. Especially since one needs to add a specific exec command to test for this. What would be interesting is maybe to add a "test" (needs better wording) that represents the test command instead of being forced to write a whole exec command.