[Patch] Remove workaround for copy_backward

[Gabriel Dos Reis]

Paolo Carlini <pcarlini@unitus.it> writes:

| Gabriel Dos Reis wrote:
| 
| >Paolo,
| >
| >As promised.
| >
| Many, many thanks for your not-sketchy-at-all posting! I will work on
| this in the next couple of weeks, both our names in the ChangeLog, of
| course ;)

Oh, I do not believe I deserve any ChangeLog entry for that rough
elaboration.  It is skecthy because I did not include discussions to
handle reverse_iterator<>s.  The person who has been doing the work is
*you* :-).  I do not anticipate any "hard" complication, though.

-- Gaby