debug algo patch

[François Dumont]

Hi

     Here is an evolution in management of debug algos I would like to 
propose for a future version. The attached patch does 3 things:
     - Move algos implementation details in std::__detail namespace so 
that whatever mode (none/debug/profile/parallel) is activated those 
details will always be found in the same namespace
     - Introduce real debug algos in std::__debug namespace
     - Generalize usage of __gnu_debug::__safe method that limit 
performance impact of debug mode

     I hope this patch to:
     - Clean code: debug stuff will be isolated in include/debug folder 
and won't pollute anymore normal implementations in include/bits. This 
is especially important with the introduction of calls to 
__gnu_debug::__base
     - Optimize debug performances because for the moment some debug 
algos or containers might have been calling internally other debug algos 
without knowing it and performing useless checks.

     For the moment this patch doesn't work in debug mode because of 
ambiguity when resolving algo calls as soon as debug containers are 
involved; std::__debug is considered thanks to namespace inlinement and 
std::__cxx1998 is considered because of ADL as debug containers are 
inheriting from normal ones that are in __cxx1998 namespace. I have plan 
to remove this inheritance relation if the patch suite you well.

     I have also restore the possibility to use both parallel and debug 
mode at the same time, I don't think there were a real reason to have 
remove this possibility. Note that when both modes are active we could 
also offer debug version of parallel specific algos, maybe one day.

     In debug code I use a _GLIBCXX_BASE_A to define the base namespace 
to target to find underlying algos implementation. In normal mode you 
will see usage of _GLIBCXX_PARALLEL_A. I am not happy with this name 
because in fact it might not be a parallel algo at all, when parallel 
mode is not active it will be the normal algo. I simply wanted to 
explicitly avoid usage of the debug algos, it will have to be enhance 
for the final patch.

     Note also that we could also got a step further in seggregation of 
code by moving concept checks outside normal algos implementation. We 
could have all algos defined directly into std namespace and then have 
an internal namespace with __debug, __parallel, __profile in it and one 
inlined depending on activated mode. This would have the advantage of:
- always consider concept checks first, so consistent error reporting 
whatever mode is activated or not
- avoid concept checks on internal algos usage

     I am considering to start the SVN binary incompatible branch with 
this patch as soon as it works.

Regards

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