[PATCH] Update backward/algo.h

[Paolo Carlini]

Hi Nathan,

my two cents: I'm prompted to remind that, after the discussion which followed
my

    http://gcc.gnu.org/ml/libstdc++/2001-12/msg00452.html

**nobody** will include ext/iterator, ext/algorithm or ext/whatever (i.e., any
of the files without .h inside include/ext) in any of the include and
include/bits files.

I must admit, that, personally, what convinced me that this is the right thing
to do was a comment from Gaby, unrelated to gmake bugs, but the final result is
the same.

Cheers,
Paolo.