Remove algorithms implementation duplications

[François Dumont]

Hi

     Here is the new patch based on Marc Glisse idea to use functors 
taking iterators rather than iterators::reference. Compare to the 
previous proposal there is no more impact on the creation of temporaries 
instances, no additional copy or move constructor. Of course there are 
additional iterators or functors copies but those types are supposed to 
be lightweight types easy to copy.

     I have taken this opportunity to also clean the instantiation of 
types used in concept checks. There have been patches recently to avoid 
instantiation of the iterator_traits type that became unused if concepts 
checks are disabled, I have clean this issue in the impacted files.

     Note also that this patch in addition to cleaning libstdc++ code 
will also benefit to our users:
     - concept check are no repeated each time an algo call an other 
algo. Now concept checks are done in Standard algo implementations and 
those implementations only use internal functions, the "__XXX" 
functions, that do not redo the checks
     - the search algo taking a predicate was not using the find_if 
algo. When I kept only one implementation of search I use the one with 
the __find_if call to benefit from its specialization for random access 
iterators.

     I also wonder if I shouldn't move all the implementation details in 
the std::__detail namespace ? Should I do it now, before eventually 
applying the patch ?

     Tested under linux x86_64 normal, debug and C++11-normal modes.

2012-07-11  François Dumont <fdumont@gcc.gnu.org>

     * include/bits/predefined_ops.h: New. Internal functors use to
     avoid algorithm duplications.
     * include/bits/stl_algobase.h, stl_algo.h, stl_heap.h: Adapt to
     use latter functors, remove many algorithm duplications.

François

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