Improve Range#dup spec

Author: eregon

spec/ruby/core/range/dup_spec.rb

@@ -2,10 +2,12 @@
 
 describe "Range#dup" do
   it "duplicates the range" do
-    copy = (1..3).dup
+    original = (1..3)
+    copy = original.dup
     copy.begin.should == 1
     copy.end.should == 3
     copy.should_not.exclude_end?
+    copy.should_not.equal?(original)
 
     copy = ("a"..."z").dup
     copy.begin.should == "a"