* include/bits/alloc_traits.h (__alloctr_rebind): Remove.
(__allocator_traits_base): New base class.
(__alloc_rebind): Reimplement in terms of detection idiom.
(allocator_traits): Derive from __allocator_traits_base. Reimplement
nested types in terms of detection idiom. Simplify SFINAE constraints
on overloaded static member functions.
* include/bits/hashtable.h (_Hashtable): Use __alloc_rebind instead
of __alloctr_rebind.
* testsuite/20_util/scoped_allocator/propagation.cc: Define rebind.
* testsuite/23_containers/unordered_set/instantiation_neg.cc: Adjust
dg-error line number.
From-SVN: r225244
