Many functions use char* where const char* should be used. I've changed this in a few function prototypes which I use while embedding python due to numerous warnings about deprecated casting from string constants to char*.

I was about to submit the very same patch :-)
I missed PyErr_NewException, but you missed the PyMapping_* methods ;)

Please look into this matter.  GCC 4.2 has arrived and it has a new
warning.  The code:

     char* kwlist[] = { "target", "encoding", NULL };

now gives a warning like:

"warning: deprecated conversion from string constant to ‘char*’"

at least when compiling in C++ mode...

This means that people have to declare it as "const char* kwlist", which
will then trigger another warning when calling
PyArg_ParseTupleAndKeywords with such a variable, because the prototype is:

PyAPI_FUNC(int) PyArg_ParseTupleAndKeywords(PyObject *, PyObject *,
                                                  const char *, char **,
...);

The "char **" should be "const char **".  ext-, any chance you could fix
that too?

There was once a rather long discussion about "const" in
PyArg_ParseTupleAndKeywords:
http://mail.python.org/pipermail/python-dev/2006-February/060689.html

If you don't read it to the end, here is the conclusion:
"""
It sounds like the right answer for Python is to change the signature
of PyArg_ParseTupleAndKeywords() back.  We'll fix it when C fixes its
const rules <wink>.
"""

"const char*" was accepted without opposition, though.

Douglas Greiman submitted many similar changes with his issue2135 patch.  
His patch also amends documentation, which is missing here.

I am adding dgreiman to the nosy list here to avoid duplication of 
effort.

I am -0 on the idea.