loaders where C code provides the loaded module.

conform the the InspectLoader ABC. Perk of this is that runpy/-m can
now work with namespace packages.

To make sure there is no issue with code that is both Python 2 and 3
compatible, there are no plans to remove the module any sooner than
Python 4 (unless the community moves to Python 3 solidly before then).

Also, improve some docstring descriptions of the 'errors' parameter.

Closes #14015.

exec runs into an error.  Prevent a regular multi-close of the /dev/null
fd when any of stdin, stdout and stderr was set to DEVNULL.

exec runs into an error.  Prevent a regular multi-close of the /dev/null
fd when any of stdin, stdout and stderr was set to DEVNULL.

Reported by Atsuo Ishimoto.

source_from_cache(), finishing the work introduced in changset
4134:9cacdb9d0c59.

module and not as a definition of what an enumeration is.

The new API require more discussion.