Close #2686.

* omp declare privates on outer loop, since inner loops are not 'omp parallel for'ified

* Changed always_allow_keywords_T295 for Py3.9

https://bugs.python.org/issue37645 appears to change some error
messages slightly (including the qualname and not just the
function name). This change just allows doctest to cope with
both the new and old messages

Closes #3330.

The pickle functions __reduce__ and __setstate_cython__ were being
visited in the module scope (where they were undeclared) rather
than the class scope where they were declared

Move slow MacOS builds higher up in the travis build matrix to make them start earlier and reduce the overall turn-over time.

Make sure we always use the correct post-analysed bases, mkw and metaclass in Python class creation by making the PyClassDefNode own it and other nodes only refer to it, rather than risking stale references in subnodes.
(Alternatively, ownership could be distributed across the subnodes, but it's a bit unclear how, and how to refer to the other subnodes then.)
Closes #3338.

Closes #3337.

Add warning that no Cython-specific tests should be added to the PEP-492 coroutine test file copied from CPython.

Closes #3335.

Includes extra information for some additional types

Closes #3330.

Closes #1427 

Move back to a matrix setup in travis.yml to avoid the long list of redundant and boring Python build setups.