Update test_httpservers to 2.7.13 (and be explicit about that version…

Update test_httpservers to 2.7.13 (and be explicit about that version on travis). Fixes #924. Works in 2.7.12, haven't yet tried 2.7.8.

Update travis to 3.6.0 final. [skip appveyor]

Clean up _DummyThread for greenlet.greenlet

This uses a weakref since it doesn't have rowlink.

Fixes #918.

Future perfect release date

* Resolve the DNS test differences.

Also document some of the known ways that c-ares is different as a
result of these test fixes.

Fixes #774.

* spurious assert statement.

* disable the ipv6 dual stack test even without ares, it has the same issue on travis ci. must have a different resolver configuration than I do.

* more dns tweaks for travis

* One small failure on travis.

Fix typo: silented --> silenced

Disable python 3 coverage on landscape, that may be what's keeping our builds from running there [skip appveyor]

Issue 904 fixes

Don't define them on 2.7.8.

Add a changelog entry.

Fixes #904

fixes #901

Update travis python

Update libev to 4.23

[skip appveyor]

Note that the previous 3.6 beta has been removed.

[skip appveyor]