Work around JRuby returning empty parameters on repeated calls.

This fixes a JRuby bug where by repeated calls to parameters on unbound
instance methods falsely return []

e.g. on JRuby 1.7.4
```Ruby
  String.instance_method(:replace).parameters
  # => [[:req]]
  String.instance_method(:replace).parameters
  # => []
```

And with this "fix"

```Ruby
  String.dup.instance_method(:replace).parameters
  # => [[:req]]
  String.dup.instance_method(:replace).parameters
  # => [[:req]]
```

lib/rspec/mocks/method_reference.rb

@@ -59,8 +59,17 @@ def method_implemented?(m)
       # definition of "implemented". However, it's the best we can do.
       alias method_defined? method_implemented?
 
-      def find_method(m)
-        m.instance_method(@method_name)
+      # works around the fact that repeated calls for method parameters will
+      # falsely return empty arrays on JRuby in certain circumstances, this
+      # is necessary here because we can't dup/clone UnboundMethods
+      if PLATFORM == 'java'
+        def find_method(m)
+          m.dup.instance_method(@method_name)
+        end
+      else
+        def find_method(m)
+          m.instance_method(@method_name)
+        end
       end
     end