[Python-3000] The grand renaming

[Christian Heimes]

Python 3.0a2 is out and some people are working on backports of Python
3.0 features to 2.6. Shouldn't we start to rename the new API functions
and files to their final names before we back merge code to 2.6?

I'm proposing to change the names and files as following. I'm willing to
make the necessary changes myself.

API methods:
PyUnicode - keep the name
PyBytes - PyByteArray
PyString - PyBytes
PyBuffer - PyMemoryView

Files:
bytesobject.[ch] - bytearrayobject.[ch]
memoryobject.[ch] - memoryviewobject.[ch]
stringobject.[ch] - bytesobject.[ch]

Christian