Reserve unknown in Ruby (#3763)

* Reserve unknown in ruby

* Revert ruby tests. Wait for cpp impl for conformance test

* Add conformance test for preserving unknown

* Add unknown field conformance test to csharp failure list.

* Fix comments

* Fix comment

* Fix comments

* Fix typo

* Use stringsink_string directly

* Mark hd unused

* Remove unused encodeunknown_handlerfunc
diff --git a/conformance/conformance_php.php b/conformance/conformance_php.php
index 2e3f783..4dc18f5 100755
--- a/conformance/conformance_php.php
+++ b/conformance/conformance_php.php
@@ -57,10 +57,10 @@
           return $response;
         }
       } elseif ($request->getMessageType() == "protobuf_test_messages.proto2.TestAllTypesProto2") {
-	$response->setSkipped("PHP doesn't support proto2");
-	return $response;
+        $response->setSkipped("PHP doesn't support proto2");
+        return $response;
       } else {
-	trigger_error("Protobuf request doesn't have specific payload type", E_USER_ERROR);
+        trigger_error("Protobuf request doesn't have specific payload type", E_USER_ERROR);
       }
     } elseif ($request->getPayload() == "json_payload") {
       try {