libstdc++: [_GLIBCXX_DEBUG] Do not consider detached iterators as value-initialized

An attach iterator has its _M_version set to something != 0, the container version. This
value shall be preserved when detaching it so that the iterator does not look like a
value-initialized one.

libstdc++-v3/ChangeLog:

	* include/debug/formatter.h (__singular_value_init): New _Iterator_state enum entry.
	(_Parameter<>(const _Safe_iterator<>&, const char*, _Is_iterator)): Check if iterator
	parameter is value-initialized.
	(_Parameter<>(const _Safe_local_iterator<>&, const char*, _Is_iterator)): Likewise.
	* include/debug/safe_iterator.h (_Safe_iterator<>::_M_value_initialized()): New. Adapt
	checks.
	* include/debug/safe_local_iterator.h (_Safe_local_iterator<>::_M_value_initialized()): New.
	Adapt checks.
	* src/c++11/debug.cc (_Safe_iterator_base::_M_reset): Do not reset _M_version.
	(print_field(PrintContext&, const _Parameter&, const char*)): Adapt state_names.
	* testsuite/23_containers/deque/debug/iterator1_neg.cc: New test.
	* testsuite/23_containers/deque/debug/iterator2_neg.cc: New test.
	* testsuite/23_containers/forward_list/debug/iterator1_neg.cc: New test.
	* testsuite/23_containers/forward_list/debug/iterator2_neg.cc: New test.
	* testsuite/23_containers/forward_list/debug/iterator3_neg.cc: New test.