Fix Controller.required_option overriding methods in 1.9.

In Ruby 1.9 the return value of `instance_methods` changed from an array
of strings to an array of symbols. So the collision check did not work.
Use the more compatible `method_defined?` method.
Ensure the same test array output between Ruby versions.

Array#to_s differs between 1.8 and 1.9, #inspect is unchanged.
Also, whitespace.