* include/ext/rope (_Rope_rep_alloc_base): Eliminate.
(_Rope_rep_base): Inherit directly from the rope allocator;
use rebinding instead of _Alloc_traits; pick up data member
from _Rope_rep_alloc_base.
(_Rope_alloc_base): Eliminate.
(_Rope_base): Inherit directly from the rope allocator; use
rebinding instead of _Alloc_traits; pick up data member from
_Rope_alloc_base.
(rope::_S_new_RopeLeaf, rope::_S_new_RopeConcatenation,
rope::_S_new_RopeFunction, rope::_S_new_RopeSubstring): Tweak.