New can_[in,de]crement_range debug checks

[François Dumont]

Hi

 Â Â Â  If not told otherwise I plan to commit attached patch tomorrow evening.

 Â Â Â  It is adding new Debug checks to find out if an output iterator 
will always be reachable while looping on an input range. Note that this 
check was already done previously by checking if the iterator was 
[in,de]crementable but it will now assert before any operation take 
place. I also need it in order to remove debug layer on the output 
iterator in a future patch.

 Â Â Â  I am also adding some tests on the std::equal algorithm because I 
plan to apply those macros to this algo too but users can append a 
special value at the end of the 2nd range to make sure it will never go 
beyond this position. Some tests are doing this and was triggering the 
Debug check.

 Â Â Â  * include/debug/macros.h (__glibcxx_check_can_increment_range): New.
 Â Â Â  (__glibcxx_check_can_decrement_range): New.
 Â Â Â  * include/debug/debug.h (__glibcxx_requires_can_increment_range): New.
 Â Â Â  (__glibcxx_requires_can_decrement_range): New.
 Â Â Â  * include/bits/stl_algobase.h (std::copy(_II, _II, _OI)): Use
 Â Â Â  __glibcxx_requires_can_increment_range.
 Â Â Â  (std::move(_II, _II, _OI)): Likewise.
 Â Â Â  (std::copy_backward(_BI, _BI, _BI2)): Use
 Â Â Â  __glibcxx_requires_can_decrement_range.
 Â Â Â  (std::move_backward(_BI, _BI, _BI2)): Likewise.
 Â Â Â  * testsuite/25_algorithms/copy_backward/debug/1_neg.cc: New.
 Â Â Â  * testsuite/25_algorithms/copy_backward/debug/2_neg.cc: New.
 Â Â Â  * testsuite/25_algorithms/copy_backward/debug/3_neg.cc: New.
 Â Â Â  * testsuite/25_algorithms/equal/debug/1_neg.cc: New.
 Â Â Â  * testsuite/25_algorithms/equal/debug/2_neg.cc: New.
 Â Â Â  * testsuite/25_algorithms/equal/debug/3_neg.cc: New.

Tested under Linux x86_64, normal and debug modes.

François

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