Per gevent/gevent#546, rebase the changes on top of gevent 1.0.2. Fixes gevent/gevent#477.

Should fix #459. See https://github.com/gevent/gevent/issues/459#issuecomment-49506870

Thanks to @snaury.

This reverts commit 12e4fb18.

Thanks to @zhangchunlin and @mvalkon.

Fix #483. Close #489.

Markdown typo correction

peek() should return the same element that get() returns, which
is not currently the case.

Add regression test for queue peek().

To prevent this:

======================================================================
FAIL: test_terminate (__main__.TestPool10)
----------------------------------------------------------------------

Traceback (most recent call last):

File "test__threadpool.py", line 176, in test_terminate

assert kill.elapsed < 0.5, kill.elapsed

AssertionError: 0.564028263092041

too slow

It was possible for IMap/IMapUnordered greenlets to exit without putting the final StopIteration. So, whoever was waiting on the results would have to wait forever (or until LoopExit if there's nothing else running in the program).

Original patch and test by @thinxer (close #424).

Fix #311: same issue.