Simplified the ICB statemachine with the addition of a lock state to handle the case of iterate() called while a
previous process() iteration is just existing.
Also added the CALLED state to replace INACTIVE when a callback is called before PENDING state entered.
renamed INACTIVE to IDLE
Made the SelectorManager use the CaS state machine for both locking and controlling
the mode of handling changes.
Replaced the concurrent change queue with a pair of array lists that are switched while the lock state is held
The HttpContent class has been reworked to store HttpField instances, we may be generated on
demand or instances of PreEncodedHttpField.
The encoding of HTTP2 fields has been generalized to handle both indexed and literal fields, selected
by header enum set.
Default servlet and response classes have been cleaned up in how they set response headers.
The state machine now simply tracks if the endpoint is selecting or has been selected.
The slight complexity is that any transition between these two states goes via a locked
state, where there is exclusive access to the interested ops and selection key.
It was possible that updateKey() was seeing a SELECTING state and
therefore attempt to call setKeyInterests(), while changeInterests()
was also seeing the SELECTING state, then moving to CHANGING so that
_interestOps was accessed concurrently.
Also made the update task to call updateKey() instead of calling
directly setKeyInterests(), in order to comply with the state
machine; this required to have onSelected() handle additional states
that are created by updateKey().
Finally, in updateKey() now setKeyInterests() is called before
updating the state to isolate the call into its own state.
Fixed IllegalStateException by handling NEED_UNWRAP for the CLOSED
state in fill().
The EOFException does not seem to be an issue with the client.
Also removed an unneeded catch block and an empty if statement.
+ HttpTester, a testing class, was used by jetty-servlets,
embedded-jetty-examples, and test-integration, all from
those testing scopes. Moved the HttpTester into the
pre-existing jetty-http "tests" classified artifact.
