Use include instead of equal assertion.

irb will load multiple rc files now. If developer have their rcfile on
home directory or etc, equal assertion will fail with custom prompt.

spec/ruby/core/binding/irb_spec.rb

@@ -11,6 +11,8 @@ describe "Binding#irb" do
       pipe.readlines.map(&:chomp)
     end
 
-    out[-3..-1].should == ["a ** 2", "100", "exit"]
+    [out[-3..-1], ["a ** 2", "100", "exit"]].transpose.each do |actual, expected|
+      actual.should include(expected)
+    end
   end
 end