Remove using-declarations that add std names to __gnu_cxx

Remove using-declarations that add std names to __gnu_cxx

These using-declarations appear to have been added for simplicity when
moving the non-standard extensions from namespace std to namespace
__gnu_cxx. Dumping all these names into namespace __gnu_cxx allows
unportable uses like __gnu_cxx::size_t and __gnu_cxx::pair, which serve
no useful purpose.

This patch removes most of the using-declarations from namespace scope,
then either qualifies names as needed or adds using-declarations at
block scope or typedefs at class scope.

	* include/backward/hashtable.h (size_t, ptrdiff_t)
	(forward_iterator_tag, input_iterator_tag, _Construct, _Destroy)
	(distance, vector, pair, __iterator_category): Remove
	using-declarations that add these names to namespace __gnu_cxx.
	* include/ext/bitmap_allocator.h (size_t, ptrdiff_t): Likewise.
	* include/ext/debug_allocator.h (size_t): Likewise.
	* include/ext/functional (size_t, unary_function, binary_function)
	(mem_fun1_t, const_mem_fun1_t, mem_fun1_ref_t, const_mem_fun1_ref_t):
	Likewise.
	* include/ext/malloc_allocator.h (size_t, ptrdiff_t): Likewise.
	* include/ext/memory (ptrdiff_t, pair, __iterator_category): Likewise.
	* include/ext/mt_allocator.h (size_t, ptrdiff_t): Likewise.
	* include/ext/new_allocator.h (size_t, ptrdiff_t): Likewise.
	* include/ext/numeric (iota): Fix outdated comment.
	* include/ext/pool_allocator.h (size_t, ptrdiff_t): Likewise.
	* include/ext/rb_tree (_Rb_tree, allocator): Likewise.
	* include/ext/rope (size_t, ptrdiff_t, allocator, _Destroy): Likewise.
	* include/ext/ropeimpl.h (size_t, printf, basic_ostream)
	(__throw_length_error, _Destroy, std::__uninitialized_fill_n_a):
	Likewise.
	* include/ext/slist (size_t, ptrdiff_t, _Construct, _Destroy)
	(allocator, __true_type, __false_type): Likewise.

From-SVN: r271807