Issue #13701: Fix decorator avoidance (due to desire for Python 2.3 compatibility) in decimal module.

Initial patch by Zachary Ware.

Initial patch by Zachary Ware.

Thanks to George Yoshida.

Thanks to George Yoshida.

Thanks to George Yoshida.

Thanks to Daniel Müllner from docs@

Thanks to Daniel Müllner from docs@

Thanks to Daniel Müllner from docs@

Patch by Stephen Tonkin.

Patch by Stephen Tonkin.

Calling OS functions can fail with errors other than FileNotFoundError: a
FreeBSD buildbot fails for example with a PermissionError.

... (unsigned long and unsigned int) to avoid an undefined behaviour with
Py_TPFLAGS_TYPE_SUBCLASS ((1 << 31). PyType_GetFlags() result type is now
unsigned too (unsigned long, instead of long).

Patch written by Serhiy Storchaka.