Use LoadError#original_message if available in depend_on

did_you_mean 1.5.0 will add suggestions to `LoadError`. This means that
`LoadError#message` will now return a new string on each invocation, and
mutating the result will no longer modify the error's message.

activesupport/lib/active_support/dependencies.rb

@@ -375,7 +375,12 @@ def depend_on(file_name, message = "No such file to load -- %s.rb")
       require_or_load(path || file_name)
     rescue LoadError => load_error
       if file_name = load_error.message[/ -- (.*?)(\.rb)?$/, 1]
-        load_error.message.replace(message % file_name)
+        load_error_message = if load_error.respond_to?(:original_message)
+          load_error.original_message
+        else
+          load_error.message
+        end
+        load_error_message.replace(message % file_name)
         load_error.copy_blame!(load_error)
       end
       raise

activesupport/test/dependencies_test.rb

@@ -42,6 +42,13 @@ def test_depend_on_path
     assert_equal expected.path, e.path
   end
 
+  def test_depend_on_message
+    e = assert_raises(LoadError) do
+      ActiveSupport::Dependencies.depend_on "omgwtfbbq"
+    end
+    assert_equal "No such file to load -- omgwtfbbq.rb", e.message
+  end
+
   def test_require_dependency_accepts_an_object_which_implements_to_path
     o = Object.new
     def o.to_path; "dependencies/service_one"; end