added a test that YAML.load doesn't get clobbered

I THINK this is a good idea? I considered multiple approaches to testing this;
what I like about this dumb way (just try to deserialize a symbol) is that it's
nice and simple.

test/test_configuration.rb

@@ -131,6 +131,11 @@ class TestConfiguration < Test::Unit::TestCase
         Jekyll.configuration({'config' => [@user_config]})
       end
     end
+
+    should "not clobber YAML.load to the dismay of other libraries" do
+      assert_equal :foo, YAML.load(':foo')
+      # as opposed to: assert_equal ':foo', SafeYAML.load(':foo')
+    end
   end
   context "loading config from external file" do
     setup do