SF # 595026: support for masks in getargs.c.

SF # 595026: support for masks in getargs.c.

New functions:
  unsigned long PyInt_AsUnsignedLongMask(PyObject *);
  unsigned PY_LONG_LONG) PyInt_AsUnsignedLongLongMask(PyObject *);
  unsigned long PyLong_AsUnsignedLongMask(PyObject *);
  unsigned PY_LONG_LONG) PyLong_AsUnsignedLongLongMask(PyObject *);

New and changed format codes:

b unsigned char 0..UCHAR_MAX
B unsigned char none **
h unsigned short 0..USHRT_MAX
H unsigned short none **
i int INT_MIN..INT_MAX
I * unsigned int 0..UINT_MAX
l long LONG_MIN..LONG_MAX
k * unsigned long none
L long long LLONG_MIN..LLONG_MAX
K * unsigned long long none

Notes:

* New format codes.

** Changed from previous "range-and-a-half" to "none"; the
range-and-a-half checking wasn't particularly useful.

New test test_getargs2.py, to verify all this.