Implement N3657: heterogeneous lookup in associative containers.

Implement N3657: heterogeneous lookup in associative containers.

	* include/bits/stl_map.h (map::find<>, map::count<>,
	map::lower_bound<>, map::upper_bound<>, map::equal_range<>): New
	member function templates to perform heterogeneous lookup.
	* include/bits/stl_multimap.h (multimap::find<>, multimap::count<>,
	multimap::lower_bound<>, multimap::upper_bound<>,
	multimap::equal_range<>): Likewise.
	* include/bits/stl_multiset.h (multiset::find<>, multiset::count<>,
	multiset::lower_bound<>, multiset::upper_bound<>,
	multiset::equal_range<>): Likewise.
	* include/bits/stl_set.h (set::find<>, set::count<>,
	set::lower_bound<>, set::upper_bound<>, set::equal_range<>): Likewise.
	* include/bits/stl_tree.h (_Rb_tree::_S_lower_bound_tr,
	_Rb_tree::_S_upper_bound_tr, _Rb_tree::_M_find_tr,
	_Rb_tree::_M_count_tr, _Rb_tree::_M_lower_bound_tr,
	_Rb_tree::_M_upper_bound_tr, _Rb_tree::_M_equal_range_tr): Likewise.
	* testsuite/23_containers/map/operations/2.cc: New.
	* testsuite/23_containers/multimap/operations/2.cc: New.
	* testsuite/23_containers/multiset/operations/2.cc: New.
	* testsuite/23_containers/set/operations/2.cc: New.

From-SVN: r219888