Use C++11 direct init in __debug::forward_list

[François Dumont]

This patch makes extensive use of C++11 direct init in 
__debug::forward_list.

Doing so I also try to detect useless creation of safe iterators in 
debug implementation. In __debug::forward_list there are severals but I 
wonder if it is worth fixing those. Most of them are like this:

 Â Â Â Â Â  void
 Â Â Â Â Â  splice_after(const_iterator __pos, forward_list& __list)
 Â Â Â Â Â  { splice_after(__pos, std::move(__list)); }

__pos is copied.

Do you think I shouldn't care, gcc will optimize it ?

I wonder if it would be ok in debug implementation to use this kind of 
signature:

void splice_after(const const_iterator& __pos, forward_list& __list)

Iterator taken as rvalue reference ?

I guess it is not Standard conformant so not correct but maybe I could 
add a private _M_splice_after with this signature.

 Â Â Â  * include/debug/forward_list
 Â Â Â  (forward_list<>::before_begin()): Use C++11 direct initialization.
 Â Â Â  (forward_list<>::begin()): Likewise.
 Â Â Â  (forward_list<>::end()): Likewise.
 Â Â Â  (forward_list<>::cbefore_begin()): Likewise.
 Â Â Â  (forward_list<>::cbegin()): Likewise.
 Â Â Â  (forward_list<>::cend()): Likewise.
 Â Â Â  (forward_list<>::emplace_after<>(const_iterator, _Args&&...)): 
Likewise.
 Â Â Â  (forward_list<>::insert_after(const_iterator, const _Tp&)): Likewise.
 Â Â Â  (forward_list<>::insert_after(const_iterator, _Tp&&)): Likewise.
 Â Â Â  (forward_list<>::insert_after(const_iterator, size_type, const _Tp&)):
 Â Â Â  Likewise.
 Â Â Â  (forward_list<>::insert_after(const_iterator, initializer_list<>)):
 Â Â Â  Likewise.
 Â Â Â  (forward_list<>::erase_after(const_iterator)): Likewise.
 Â Â Â  (forward_list<>::erase_after(const_iterator, const_iterator)): Likewise
 Â Â Â  and ensure consistent iterator comparison.

Tested under Linux x86_64, Debug mode and committed.

François

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