Added news about new operator overloading and __getattr__ etc.

Added copyright.tex to all files.
Added descr of check_interval to libsys.tex.
Corrected lotsa typos in tut.tex (thanks to George M. Sipe).
Corrected mktuple (should be newtupleobject) example in ext.tex.

Added some new demos.  Fixed a few others.

Removed a few diagram breaks since Kees' program is now cleverer

macosmodule.c: lots of updates (though playing sound can still hang :-( )

	* Modules/(posix,socket}module.c: more NT changes

	global: Py_MakePendingCalls.  Also guard against recursive calls

	* Include/classobject.h, Objects/classobject.c,
	Python/{ceval.c,bltinmodule.c}: 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)