Move to the safer __cinit__ for all watchers.

Now that the base watcher has access to its libev ev_watcher pointer, start moving the properties there, starting with ref.

We no longer need to gc before getting a libuv io object on PyPy: everything is deterministically closed (or should be).

Debugging for a weird EPERM error in test__fileobject.py on travis with libuv; not seen locally or on appveyor [skip appveyor].

And must be close() when done. The IO watchers already required this
for libuv; doing it for everything simplifies memory management and
object lifetimes and lets us get rid of a bunch of weakref objects
with callbacks.

This is a new requirement and will only affect those that use
CFFI (e.g., PyPy) and specifically it's needed for libuv; libev
doesn't really do much with it.

Some debugging help for forgetting to close objects piggybacks on
tracemalloc on Python 3.

test_ftplib.py fails in Python 3 because of some warnings about
unclosed objects.
test__backdoor.py fails in Python 2 for the same reason.

[skip appveyor]

GEVENTSETUP_EV_VERIFY has to be set when gevent is compiled. Move it from the 'leaktest' target down to where we call develop

This lets us start using our infrastructure for flaky timeouts.

Make Timeout._start_new_or_dummy stop forcing the issue.

The failing test_telnetlib was fixed by avoiding a zero-duration timer. On libuv zero duration timers can block the event loop.

libev follows libuv by not updating the loop time in a timer by default. A Timeout that we use internally still does this though.

correct a typo in src/gevent/greenlet.py
[skip ci]