truncation behavior of floating point formatting

	* Doc/ref3.tex: clarify defaults for __repr__, __cmp__ and
	__str__; correct (some) descriptions of class constructors

is now also optional

Python

Emacs.

is the last thing on the line.

Documented new formatting features: %s takes any type, and
'%(key)format' % dictionary.
Documented posixpath.expandvars().