[ISSUE #86] fixed GetMessageStoreTimestamp not return StoreTimestamp

[ifplusor]

What is the purpose of the change

fixed the bug #86
GetMessageStoreTimestamp not return StoreTimestamp

Brief changelog

-    return ((MQMessageExt *) msg)->getBornTimestamp();
+    return ((MQMessageExt *) msg)->getStoreTimestamp();

Verifying this change

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