Fix removing class methods between 1.8 and 1.9

#instance_methods in 1.8 returns strings, not symbols. Most recommend
using method_defined? instead of #instance_methods.include?, however,
#method_defined? doesn't allow filtering of inherited methods.

So, we switch back to using #method_defined? which means we need to
handle the 'method not defined on class' error another way...

Use #undef_method in place of #remove_method which will undefine
inherited methods as well. This is what we should have done all along.

The parent class method is still defined as expected. #undef_method only
hides that implementation from the subclass so it doesn't attempt to
defer to the parent class. This allows a safe #define_method on the
subclass.

Author: jasonkarns

lib/gimme/spies_on_class_methods.rb

@@ -10,9 +10,9 @@ def spy(method)
       meta_class = (class << @cls; self; end)
       method = ResolvesMethods.new(meta_class, method).resolve(@raises_no_method_error)
 
-      if meta_class.instance_methods(false).include? method
+      if meta_class.method_defined? method
         Gimme.class_methods.set(@cls, method)
-        meta_class.send(:remove_method, method)
+        meta_class.send(:undef_method, method)
       end
 
       cls = @cls