Preserve ability to inherit from original error

#396 (comment)

lib/active_resource/exceptions.rb

@@ -36,12 +36,7 @@ def to_s; @message ; end
   end
 
   # Raised when a Errno::ECONNREFUSED occurs.
-  class ConnectionRefusedError < ConnectionError
-    def initialize(message)
-      @message = message
-    end
-    def to_s; @message ; end
-  end
+  class ConnectionRefusedError < Errno::ECONNREFUSED; end
 
   # 3xx Redirection
   class Redirection < ConnectionError # :nodoc:

test/cases/connection_test.rb

@@ -289,6 +289,13 @@ def test_handle_econnrefused
     assert_raise(ActiveResource::ConnectionRefusedError) { @conn.get("/people/1.json") }
   end
 
+  def test_handle_econnrefused_with_backwards_compatible_error
+    http = Net::HTTP.new("")
+    @conn.expects(:http).returns(http)
+    http.expects(:get).raises(Errno::ECONNREFUSED, "Failed to open TCP connection")
+    assert_raise(Errno::ECONNREFUSED) { @conn.get("/people/1.json") }
+  end
+
   def test_auth_type_can_be_string
     @conn.auth_type = "digest"
     assert_equal(:digest, @conn.auth_type)