* include/std/bitset (bitset<>::all): Add, per DR 693 [Ready].
(_Base_bitset<>::_M_are_all_aux()): Add.
* include/debug/bitset (bitset<>::all): Add.
* testsuite/23_containers/bitset/all/1.cc: New.
* docs/html/ext/howto.html: Add an entry for DR 693.
* include/std/bitset (bitset<0>::set, reset, flip, test): Remove,
not necessary anymore.