extend only the result instance's eigenclass, not all instances of that instance's type

So basically, bitbucket extends EVERY INSTANCE OF THE CLASS OF env[:body]. So, in our case, env[:body] is sometimes a string or an array, and from then on, ANY string will have bitbucket result methods.

This patch will only extend the eigenclass of the instance, meaning only that instance will have the methods, not all instances of the same class.