[Python-3000] Removal of PyArg_Parse()

["Martin v. Löwis"]

> Then I don't think it's a priority to try to get rid of it, and maybe
> it should just stay.

I think it would be desirable to get rid of METH_OLDARGS. Ideally, this
should already be possible, as all modules should have been changed to
be explicit about their usage of METH_OLDARGS (rather than relying on
the struct field defaulting to 0), this can be "verified" by running the
test suite once and checking that all ml_flags have one of METH_VARARGS,
METH_NOARGS or METH_O set.

Then it would be possible to drop METH_VARARGS, declaring that a 0
value of ml_flags means the default, which is "arguments are passed
as a tuple".

As for the remaining 50 or so PyArg_Parse calls: most of them convert
a single object to some C representation; it should be possible to
use the proper underlying conversion function.

For example:
- dbm/gdbm convert using s#; this can be replaced with the buffer
  API.
- the array module converts the values on setitem using PyArg_Parse;
  these can be replaced with PyInt_AsLong, except that PyArg_Parse
  also does a range check, which could be moved into a range-checking
  function in arraymodule.

As for the case of timemodule: the surprising feature is that
"(ii)" uses PySequence_Getitem to access the fields, whereas
PyArg_ParseTuple uses PyTuple_GET_ITEM, so it won't work for
StructSequences.

Regards,
Martin