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The attached patch will fix the range-checking-code of the
integer pack functions for 64 and 32 bit architectures
(tested on i386 and Sparc64, 64-bit little-endian was not
tested 'cause of lack of hardware). All test cases worked as
expected, there is no more need for BUGGY_RANGE_CHECK.

I'm a bit unsure about the used method to get an unsigned
long from a Python_Long object with overflow checking... 
PyLong_AsUnsignedLong(PyLong_FromLong(PyInt_AS_LONG(v))) 
looks a rather excessive.