event_machine: join reactor_thread if it is already running

...rather than falling through worker_loop

Prior to the application of this patch, if an EventMachine
reactor_thread has already been started elsewhere before the
worker_loop is entered, the worker_loop exits as a second call
to EM.run does not block the current thread.

This patch causes the worker_loop thread to join the
reactor_thread if it is running.

[ew: commit message formatting]

Signed-off-by: Eric Wong <normalperson@yhbt.net>
t/GNUmakefile: cleanup test dependencies

The missing random_blob dependency was causing the following
to fail on a fresh clone:

	make -C t ThreadPool.t0005-large-file-response.sh
Rainbows! 4.4.3 - bugfixes for EventMachine users

This release fixes two EventMachine bugfixes from Lin Jen-Shin
and Mark J. Titorenko.  There are also some minor cleanups.

Lin Jen-Shin (1):
      event_machine: avoid close on deferred response

Mark J. Titorenko (1):
      event_machine: join reactor_thread if it is already running

Eric Wong (2):
      event_machine: cleanup confusing assignment
      t/GNUmakefile: cleanup test dependencies
epoll: ensure closing of pipelined clients if required

on_read normally relies on the close checking in on_readable,
but on_deferred_write_complete may be called from on_writable
instead (bypassing the close check of on_readable).

This affects both Epoll and XEpoll users, but only if they
were sending responses via body#to_path and triggering
on_deferred_write_complete.

While we're at it, favor non-recursive want_more instead of
calling on_readable recursively in ev_write_responses to
prevent stack growth.