Avoid potential reference cycles by pickling the tracebacks a Greenlet stores

Patch subprocess by default. Fixes #466.

Make the BaseServer's repr again show a handle if it's *not* an instancemethod and add a test case for the various possibilities. Update the changelog.

Version the greenlet dependency in setup.py to the latest (which was required by gevent 1.0.2 as well).

Remove the in-code checking for greenlet version in gevent.hub to avoid repetition (the version it was checking for was released in 2011).

Fixes #435.

Version the greenlet dependency in setup.py to the latest (which was required by gevent 1.0.2 as well).

Remove the in-code checking for greenlet version in gevent.hub to avoid repetition (the version it was checking for was released in 2011).

Fixes #435.

This avoids ref cycles and lets us stop manually clearing tracebacks in some test cases. The cost is the time taken to pickle/unpickle the traceback.

This most importantly fixes build issues related to C11 which is used in
for example OS X 10.11 ("El Capitan"):

    libev/ev.c:1029:42: error: '_Noreturn' keyword must precede function declarator
      ecb_inline void ecb_unreachable (void) ecb_noreturn;
                                             ^~~~~~~~~~~~

Add original tracebacks when re-raising an exception from another greenlet

Also some greenlet module cleanups.

Fixes #450. Fixes #528.

Make JoinableQueue.join consistent when items are passed to the constructor, extending #554; add a test for this.

Note that Python 2.5 support has been dropped. Add version and implementation classifiers to setup.py; make setup.py PyPy/Py3 friendly and not leak open files. [skip ci]