When detecting an invalid system configuration for overflow checks, at least print a warning, instead of leaving a dangling live exception behind.

The current code fails to compile with:

<source>:3:54: error: invalid operands to binary expression ('enum E' and 'enum E')
const enum E neg_one_class_29 = (enum E) ((enum E) 0 - (enum E) 1);
                                          ~~~~~~~~~~ ^ ~~~~~~~~~~

This change reverts to the code that was before #2186 but silences erroneous GCC warning enabled by -Wconversion (which is not a part of -Wall).

Fixes #2749

This fixes Github issue #2819.

Fix support for C++ enum classes

warning C4244: 'initializing': conversion from 'double' to 'float', possible loss of data

Fix msvc compiler warning C4244

Pointer buf cannot be NULL

warning C4244: 'initializing': conversion from 'double' to 'float', possible loss of data

Clean up insertion points after use in prange code since they conflict with the deep-copying that with-statements use for their finally-clause.
Closes GH-2780.

Avoid useless "div by zero" checks in optimised constant division code. Also avoid using a (named) C macro where code generation will do.
See GH-2820.

Fix exception messages for float division by zero, as well as their tests (which were wrong in Py2.6).

Closes #2820.

Remove superfluous code

Simplify logical expression

Fix casting ssize_t to unsigned

See #2818.

Pointer buf cannot be NULL

Clarify that extension types which implement "__cinit__" do not require their base types to implement it.
Closes #2809.

Speed up multiplication of Python numbers with small integers (<= 2**30)