- Add more accurate available() method, using a new action (still very cheap to invok...

- Add more accurate available() method, using a new action (still very cheap to invoke, and quite simple).
- This is mostly useful for Comet, since it can be difficult to know for sure if reading is possible without
  blocking if the beginning of the entity body was sent along with the request header in a single packet.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc6.0.x/trunk@533164 13f79535-47bb-0310-9956-ffa450edef68