[skip ci]

And stop a fresh greenlet from even running.

Fixes #1473.

Free user-provided resources as soon as the greenlet is cancelled, if it's not running.

Fix potential crashes in the FFI backends if a watcher was closed and…

Fix potential crashes in the FFI backends if a watcher was closed and stopped in the middle of a callback from the event loop and then raised an exception.

This could happen if the hub's ``handle_error`` function was poorly customized, for example.

Fixes #1482

Direct error handling through the loop in the unexpected-but-closed case as well.

Fix threadpool in command line scripts

Keep the actual greenlet objects, not just a counter. This way we can clean up after them better.

Only happens on Travis. Recently, the failure has started including 'Fatal Python error: PyImport_GetModuleDict missing'.

Fixes #1484.

In general, fixes any use of gevent.monkey.get_original() in such a process.

Be more careful about double-patching in general too. Detecting duplicate arguments to patch_all only patches things that need to be patched.

Fix an interaction between the switch interval and libuv that could introduce delays for large batches of callbacks

Fix an interaction between the switch interval and libuv that could introduce delays processing large batches of callbacks.

Specifically, a .3 (idle signal timer) delay as UV_RUN_ONCE would pause if there was no other active timer or IO watcher.

Now, if there are still batches of callbacks to run, we explicitly use UV_RUN_NOWAIT to only poll for IO and queue callbacks without waiting at all.

This gets the time for the synthetic greenlet-launching benchmarks to match libev-cffi and be close to libuv-cext.

Fixes #1493

Current results:

| Benchmark             | gevent-libev-cext | gevent-libev-cffi             | gevent-libuv-cffi               |
|-----------------------|-------------------|-------------------------------|---------------------------------|
| gevent spawn          | 12.5 us           | 13.7 us: 1.10x slower (+10%)  | 14.2 us: 1.14x slower (+14%)    |
| gevent sleep          | 2.09 us           | 3.16 us: 1.51x slower (+51%)  | 74.4 us: 35.64x slower (+3464%) |
| geventpool sleep      | 3.46 us           | 6.20 us: 1.79x slower (+79%)  | 151 us: 43.58x slower (+4258%)  |
| geventraw spawn       | 5.34 us           | 6.54 us: 1.22x slower (+22%)  | 6.38 us: 1.19x slower (+19%)    |
| geventraw sleep       | 949 ns            | 1.66 us: 1.75x slower (+75%)  | 43.9 us: 46.25x slower (+4525%) |
| geventpool join       | 1.57 us           | 3.43 us: 2.18x slower (+118%) | 88.2 us: 56.07x slower (+5507%) |
| gevent spawn kwarg    | 14.2 us           | 12.4 us: 1.15x faster (-13%)  | 14.8 us: 1.04x slower (+4%)     |
| geventraw spawn kwarg | 7.68 us           | 8.38 us: 1.09x slower (+9%)   | 8.47 us: 1.10x slower (+10%)    |
| none spawn kwarg      | 771 ns            | 738 ns: 1.04x faster (-4%)    | 734 ns: 1.05x faster (-5%)      |

Not significant (3): geventpool spawn; none spawn; geventpool spawn kwarg

Refs #1493

Still needs better docs.

Improve safety for libuv async and idle watchers.

Fixes #1489.

gevent.pywsgi: Support keep-alive in HTTP/1.0

With tests. Supercedes #1331.

Remove redundant checks for constant values.

Make Semaphores fair.

Preserve order of wakeups. Take steps to avoid going back to the O(n^2) old behaviour, though, much like Greenlet does.

This means we auto-unlink links as we call them. Most users won't notice as that's a very low-level method, but baseserver.py was relying on the same rawlink being called every time a semaphore became ready. That was *a lot*, so this eliminates some calls.

coveralls 1.9 is incompatible with coverage >= 5.0a5

Fix #1464 and fix #1465 by making LockType sleep on failure to non-blocking acquire the lock.

Using sleep doesn't force a trip around the event loop until the switch interval elapses.

More simplification and unification of the file objects

Keeping control this way simplifies and unifies the implementations.

- Fix a concurrency bug in FileObjectPosix that we were hiding with buffering and a RuntimeError.
- Add all the error checking the stdlib does, with a few exceptions that make sense.

See #1441.