Perl Bindings: Set serialization/deserialization differs

In the Perl bindings, a Thrift Set is dezerialized as a hashref, but the serialization code expects an arrayref. This causes the code to die when called if attempting to serialize a previously dezerialized Set.

Additionally, it looks like there is a typo in the test that is testing this feature:

https://github.com/apache/thrift/blob/49f4dc0cd8c87213a0f80ae1daba2d094a358ea7/test/perl/TestClient.pl#L262

If you change that @$setout to @$setin, the test fails.

It doesn't make much sense to implement a Set in Perl as array, because arrays allow duplicate entries and are ordered.

I've written a change for the serialization that correctly expects a hashref: https://github.com/apache/thrift/pull/831