raise an ImportError (rather than fatal) when __import__ is not found in __builtins__ (closes #17867)

modules which will typically work when reloaded.

A hack is used to support these functions as their API allowed them to
pass in a file object but then operate as if import had loaded them.
Unfortunately the hack kept a reference around for the file object
passed in which would be unusable on reload since it had been closed.
The solution is to simply use the hack for the initial load but then a
proper loader on the module so that imp.reload() at least has a chance
to work.

I know one of them looks worse, but now it is <80 chars and
matches the 2.7 text.

Behavior confirmation and initial patch by Jessica McKellar.

Original patch by Kushal Das.

such as was shipped with Centos 5 and Mac OS X 10.4.

importlib.invalidate_caches().

Without this changeset plistlib would write empty tags for plistlib.Data
objects in deeply nested datastructures.

Fixes #17353

condition variable.  Original patch by Thomas Rachel.

Patch by Jonas Wagner

Patch by Jeremy Kloth.

to correctly process the opcode when it is used on non-list objects.

Patch by Ingrid Cheung and Brendan McLoughlin.

- Issue #17782: Fix undefined behaviour on platforms where ``struct timespec``'s "tv_nsec" member is not a C long.

registry does not grow exponentially with generation of process.