* include/debug/helper_functions.h
	(__gnu_debug::_Safe_iterator<>): Add declaration.
	(__can_advance(_Ite, _Size)): New.
	(__can_advance(const _Safe_iterator<>&, _Size)): Overload declaration.
	* include/debug/functions.h
	(__gnu_debug::_Safe_iterator<>): Remove declaration.
	* include/debug/stl_iterator.h
	(__can_advance(const _Safe_iterator<>&)): New definition.
	* include/debug/stl_iterator.h
	(__can_advance(const std::reverse_iterator<>&, _Size)): New.
	(__can_advance(const std::move_iterator<>&, _Size)): New.
	* include/debug/macros.h (__glibcxx_check_can_increment): New.
	* include/debug/debug.h (__glibcxx_requires_can_increment): New.
	* include/bits/stl_algobase.h (fill_n): Use latter.
	* testsuite/25_algorithms/fill_n/2.cc: New.
	* testsuite/25_algorithms/fill_n/debug/1_neg.cc: New.
	* testsuite/25_algorithms/fill_n/debug/2_neg.cc: New.
	* testsuite/25_algorithms/fill_n/debug/3_neg.cc: New.
	* testsuite/25_algorithms/fill_n/debug/4_neg.cc: New.

From-SVN: r261566