Add the username in the quotation private message.

According user story, if user reply on private message with quote, we add ">>" symbol before string.
But it is not informative if we have chain of message with quoting.
For example, user1 send message("initial message")to user2.
user2 quote message, add "answer1" to message body and reply.
user1 will see:
>>initial message
answer1
It is still ok now.
Later, user1 also quote message and add "answer2" to message body and reply.
user2 will see:
>>initial message
>>answer1
answer2
Further-more. We can see something like:
>>initial message
>>answer1
>>answer2
>>answer3
>>answer4
answer5
It is very inconvenient and easily confused who owns this or that part of message.

We can format reply somehow like:
>> From: user1
>> Date: Sun, 24 Jul 2011 16:45:31
>> initial message