Break the include method for better binary backward compatibility

Hi Richard,

Scalachek is used by numerous projects, especially in conjunction with Scalaz and I had some run-time errors when running the latest specs2 version, which depends on ScalaCheck 1.12.0 and the Scalaz-ScalaCheck bindings to test laws in Scalaz because of the new include method.

Breaking it in 2 should solve the problem. That would be nice if you could publish this as 1.12.1 when you have a minute.

Thanks.

cc/ @larsrh