Review action code usage across HTTP and AJP processors
- remove the unused POST_REQUEST action
- align ordering between AJP and HTTP for easier comparison
- add missing actions to AJP for implementation / review (see TODOs)
- document known NO-OPs for AJP
- ensure trying to use comet over AJP triggers an error

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1518926 13f79535-47bb-0310-9956-ffa450edef68