Misleading comment in prologue of ReorderBufferQueueMessage

The name of the function suggests that the given message will be queued in ReorderBuffer. The prologue of the function says so too

 776 /*
 777  * Queue message into a transaction so it can be processed upon commit.
 778  */

It led me to think that a non-transactional message is processed along with the surrounding transaction, esp. when it has an associated xid.

But in reality, the function queues only a transactional message and decoders a non-transactional message immediately without waiting for a commit.

We should modify the prologue to say

"Queue a transactional message into a transaction so that it can be processed upon commit. A non-transactional message is processed immediately." and also change the name of the function to ReorderBufferProcessMessage(), but the later may break API compatibility.

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