entirely redone operator overloading.  The rules for class
	instances are now much more relaxed than for other built-in types
	(whose coerce must still return two objects of the same type)

	* Objects/floatobject.c: add overflow check when converting float
	to int and implement truncation towards zero using ceil/float

	* Objects/longobject.c: change ValueError to OverflowError when
	converting to int

	* Objects/rangeobject.c: modernized

	* Objects/stringobject.c: use HAVE_LIMITS instead of __STDC__

	* Objects/xxobject.c: changed to use new style (not finished?)