Signed-off-by: Stefan Behnel <stefan_ml@behnel.de>

The change of making "tstate->exc_state" a struct was introduced in CPython 3.7.0a3 and not 3.7.0a2, which some people still seem to be using right now.

Add safety checks to prevent exception subtype checks with non-types. This raises a TypeError in Py3 now and we should handle that at some point.

Closes #2425.

Fix: reallowing tp_clear() in a subtype of an @no_gc_clear extension type generated an invalid C function call to the (non-existent) base type implementation.
Closes #2309.

This reverts commit eb0e4666.

Fix error reporting on very early errors when the Cython runtime configuration module is not set up yet.
See #2199.

Avoid segfault due to a bug in g++ 4.4.7 when the -Os setting for the module init function is enabled.
Closes #2235.

Closes #1771.

Bug fix for boolean return using statement with internal commas.

Avoid uninitialised C variable (and thus potentially undefined behaviour), even if it's not actually being used in that case.

Improve libcpp.unordered_map API

Add zip_safe=False to userguide setup.py

Misc. typos

Closes #2194.

Closes #2193.