424743 - Verify abort behavior in case the total timeout expires
before the connect timeout.

The changes to fix this issue uncovered problems in the HttpSender
state machine.
In particular, the SenderState is now defining more states that
depend on deferred content, and on handling of 100 Continue responses.

The refactoring also highlighted the fact that there was no need to
keep HttpConversation objects in a Map in HttpClient: they are now
only referenced by the HttpRequest.
With this change, Request.getConversationID() has been deprecated.

Also fixed a number of tests to make them more reliable.