Issue 667770: import C API mess

There are too many different C-level APIs for importing
a module.

Many of them have the nasty property that they can try
to do a relative import in the context of the nearest
Python stack frame, where that is not what the C code
intended.

This needs to be cleaned up.

Example use case: time.strptime() is now a C wrapper
that imports the _strptime module; but if you follow
the path it takes to import, it's quite an amazing
journey. It should cut all of that short by looking in
sys.modules['_strptime'] first. (But what about
restricted execution? Well _strptime.py ought to be safe.)

Brett, perhaps you can consider this with your integration of
import-rewritten-in-Python?  I think it's fine to leave this alone for 2.6.

I was planning to do that in order to make my life simpler when I have
to re-implement the C API.

The story of impports from the C level is much more sane than back in the 2.6 days thanks to PyImport_Import, PyImport_ImportModuleLevelObject, and PyImport_ImportModuleLevel.

stage: needs patch -> resolved