This bug covers some general improvements to ObjectIn/OutStream.

More specifically:
 - Reuse the existing StringBuilder instance, where possible.
 - Skip primitive/object reading/writing if no primitives/objects in the stream/class.
 - For clarify and readability, SerialCallbackContext.checkAndSetUsed()
   should be invoked directly. It makes it very clear what the intent is.
 - General cleanup.

see mail discussion on:
  http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-January/024778.html
  http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-February/024817.html
  http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-February/024860.html