Farewell, pointless roundtrips, we hardly knew ye.

Hoped to avoid it, but it's the obvious solution for Ansible.

This isn't nearly enough, but it catches the most common victim of
EINTR.

It looks ugly as sin, but this nets about a 20% drop in user CPU time,
and close to 15% increase in throughput.

The average log call is around 10 opcodes, prefixing with '_v and' costs
an extra 2, but both are simple operations, and the remaining 10 are
skipped entirely when _v or _vv are False.

This matches their respective functions under test, which now reside in
mitogen.parent.

Tests should now match changes in
4d31300dd09ae7aaa394e53a48102167521f3f91

Since f44356af3275912f7df78fa58e860f107a71e7e5 mitogen.core.Importer()
takes a Router instance.

As of adc8fe3aed470de55a6e5ea3d7c6a31f7c6d1ff1 Receiver objects do not
have a get_data() method and Receiver.get() does not unpickle the
message.

As of adc8fe3aed470de55a6e5ea3d7c6a31f7c6d1ff1 Receiver objects do not
have a get_data() method and Receiver.get() does not unpickle the
message.

Turns out it is far too easy to burn through available file descriptors,
so try something else: self-pipes are per thread, and only temporarily
associated with a Lack that wishes to sleep.

Reduce pointless locking by giving Latch its own queue, and removing
Queue.Queue() use in some places.

Temporarily undo merging of of Waker and Latch, let's do this one step
at a time.

On Python 2.x, operations on pthread objects with a timeout set actually
cause internal polling. When polling fails to yield a positive result,
it quickly backs off to a 50ms loop, which results in a huge amount of
latency throughout.

Instead, give up using Queue.Queue.get(timeout=...) and replace it with
the UNIX self-pipe trick. Knocks another 45% off my.yml in the Ansible
examples directory against a local VM.

This has the potential to burn a *lot* of file descriptors, but hell,
it's not the 1940s any more, RAM is all but infinite. I can live with
that.

This gets things down to around 75ms per playbook step, still hunting
for additional sources of latency.

Now featuring one roundtrip per module invocation.