Adjust extension types to use allocator_traits

Adjust extension types to use allocator_traits

This makes these extensions work with types meeting the Cpp17Allocator
requirements as well as the C++98 Allocator requirements.

	* include/backward/hash_set (hash_set): Use __alloc_traits.
	* include/backward/hashtable.h (_Hashtable): Likewise.
	* include/ext/alloc_traits.h (__alloc_traits::allocate): Add overload
	taking a hint.
	* include/ext/extptr_allocator.h (_ExtPtr_allocator::allocate): Ignore
	hint.
	* include/ext/slist (_Slist_base): Use __alloc_traits.
	* include/tr1/hashtable.h (_Hashtable): Likewise.
	* include/tr1/regex (match_results): Use vector::const_reference
	instead of assuming the allocator defines it.
	* testsuite/backward/hash_map/23528.cc: Use allocator_traits in C++11.
	* testsuite/tr1/6_containers/unordered_map/capacity/29134-map.cc: Use
	__gnu_test::max_size.
	* testsuite/tr1/6_containers/unordered_multimap/capacity/
	29134-multimap.cc: Likewise.
	* testsuite/tr1/6_containers/unordered_multiset/capacity/
	29134-multiset.cc: Likewise.
	* testsuite/tr1/6_containers/unordered_set/capacity/29134-set.cc:
	Likewise.

From-SVN: r277335