Reconsider calling close() of the previous assigned stream or channel in MessageBuffer(Input|Output)#reset #173

In #169 and #170, we made some changes to call a previously assigned stream or channel instead of a new one passed as a parameter.

But I found https://github.com/spring-projects/spring-framework does the followings when it returns a HTTP request with jackson-dataformat-msgpack.

• Reuses an OutputStream (org.apache.catalina.connector.CoyoteOutputStream) without having called its close()
  • Of course, it includes a new SocketChannel each time
• Creates a new org.msgpack.jackson.dataformat.MessagePackGenerator
  • Which calls org.msgpack.core.buffer.OutputStreamBufferOutput#reset internally except for the first time

As a result, the OutputStream the framework tries to reuse will be closed unexpectedly and MessagePack fails to write data to it.

Also, on second thought, I think MessageBuffer(Input|Output)#reset shouldn't close the previous output or channel for the following reasons.

• Closing the previous output or channel in the methods is unexpected behaviour for the user and we can't know what it causes (it depends on their implementation)
• Releasing those resources are basically the user's responsibility

Also, on second thought, it sounds MessageBuffer(Input|Output)#reset shouldn't close the previous output or channel for the following reasons.

@xerial What do you think? If the above ideas sound good, I can fix this issue easily.