Issue #14308: Fix an exception when a dummy thread is in the threading module's active list after a fork().

Issue #14308: Fix an exception when a "dummy" thread is in the threading module's active list after a fork().

Patch by Stefan Behnel.

It is now possible to use a custom type for the __builtins__ namespace, instead
of a dict. It can be used for sandboxing for example.  Raise also a NameError
instead of ImportError if __build_class__ name if not found in __builtins__.

_multiprocessing.win32 modules now live in a single module "_winapi".
Patch by sbt.

   in order to understand the algorithm anyway.

2) v->exp == -v->digits may be assumed.

3) Fix comment (v always shares data with a).

rightfully states that an mpd_t with a coefficient flagged as MPD_CONST_DATA
must not be in the position of the result operand. In this particular case
several assumptions guarantee that a resize will never occur in all possible
code paths, which was the reason for using MPD_CONST_DATA and saving an
instruction by omitting the initialization of tmp.alloc.

For readability, tmp is now flagged as MPD_STATIC_DATA and tmp.alloc
is initialized.

Being able to overload a sys.module entry during import of a module was broken
by this changeset.

Add INCREFs, fix args->kwargs, and a second args==NULL check was removed,
left over from a merger with another function. Instead, checking msg==NULL
does what that used to do in a roundabout way.

in importlib.

Thanks to PJE for pointing out the issue and Nick Coghlan for filing
the bug.

or __name__ are not set in globals.

Thanks to Stefan Behnel for the bug report.

chown() to root under certain circumstances.