[Import-SIG] backport of importlib

[Eric Snow]

So I've gone ahead and written a (naive and probably incomplete)
script that backports importlib to 2.x[1].  There were a few syntax
differences, a couple of modules were new or had new functions, and I
had to reintroduce the old-style relative imports.

I'm hoping this will allow PEP 382 and the import engine to both be
backported simply by running this script on the implementation out of
3.3.  This was definitely a good exercise in getting familiar with the
importlib implementation.

-eric

[1] http://pypi.python.org/pypi?:action=display&name=backport_importlib