Part of reverting most of r63675 per the mailing list discussion.

occurances of PyBytes_ in the code to their original PyString_ names.  The
bytesobject.c file will be renamed back to stringobject.c in a future checkin.

NameErrors pointed out by Giampaolo.

Add an optional 'offset' parameter to byref, defaulting to zero.

issues in: 909005 and 17361001, as well as completely as possible issues
539444, 760475, 777588, 889153, 953599, 1025525, 1063924, and 658749.
This patch also includes doc and test updates as necessary.

Cleaned up the unit test.

 http://mail.python.org/pipermail/python-dev/2008-June/079988.html

Python 2.6 should stick with PyString_* in its codebase.  The PyBytes_* names
in the spirit of 3.0 are available via a #define only.  See the email thread.

Add a note about using the new AST module.

to ease standalone use of the algorithm.

more robust.