travis: we should hear it if Py3.6-dev ever starts failing. (And we should eventually remove it, but it feels too early right now.)

Hard switch off IPython test if import fails. Could not find a better way to keep it from failing on appveyor.

PyPy3: Register module cleanup with atexit

Travis-CI: Setup macOS builds

Use complete IPython dependency path in test runner to work around current test failures under appveyor.

Closes #1930.

Simplify preprocessor code that avoids the "fallthrough" C compiler warnings, assuming that "__has_attribute()" is widely supported these days. At least GCC 5.x and clang seem to have it.
Closes #1930.

Closes #1930.

Fix the first argument special method signatures of "__eq__", "__lt__" and the other richcmp methods to be of "self" type, in accordance with to the CPython specs.
See https://docs.python.org/3/reference/datamodel.html#emulating-container-types
Closes #1935.

Remove overambitious constant folding of comprehensions when they occur in a boolean context. Never assume that they are empty, since the iteration might already have required side-effects.
Closes #1920.

Closes #1916.

Considered to make it a warning, but CPython's forgiving behaviour seems unhelpful.  Can still make it a warning later.
Closed #1905.

Fix compiler crash when analysing a complex name as a type using sizeof(X) translation. Requires type analysis before the "arg_type" is set.
Closes #1908.

Prevent config lookup of "C line in traceback" option from clearing the live exception and calling setattr() with a live exception set.
Closes #1907.

Closes #1906.