stl_iterator.h (operator-(const reverse_iterator<>&, const reverse_iterator<>&), [...]): Use the auto -> return type syntax, implement DR 685.

2008-10-07  Paolo Carlini  <paolo.carlini@oracle.com>

	* include/bits/stl_iterator.h (operator-(const reverse_iterator<>&,
	const reverse_iterator<>&), operator-(const __normal_iterator<>&,
	const __normal_iterator<>&), operator-(const move_iterator<>&,
	const move_iterator<>&)): Use the auto -> return type syntax,
	implement DR 685.

From-SVN: r140937