[PATCH] Update backward/algo.h

[Benjamin Kosnik]

> When did it become a non-issue?  And, how?  

The Makefiles already install non-.h headers. See 'include/std/*' and 
include/Makefile.am. The make install rules for headers are not the make 
defaults (for other reasons, actually.)

> Should the rule not then be removed from HEADER_POLICY?  

Yes.

> Note there are many extra files that exist solely to conform 
> to the rule.  Absent the rule they should be deleted.

Can you spec this out this work please?

-benjamin