Change visibility protected methods to private in multiple classes.

The only major benefit of protected scope is that other objects of the
same type (or inherited type) can access protected methods be accessed.
In Ruby's case, private methods on a superclass can be accessed in a
subclass, unlike Java's visibility rules. Blame old Java muscle memory
here, fans.

References:

* http://tenderlovemaking.com/2012/09/07/protected-methods-and-ruby-2-0.html
* http://stackoverflow.com/questions/3534449/why-does-ruby-have-both-private-and-protected-methods