Make ext allocators support heterogeneous equality comparison

Make ext allocators support heterogeneous equality comparison

The Allocator requirements include the ability to compare different
specializations of the same allocator class template. This did not work
for __gnu_cxx::new_allocator and other extension allocators.  This patch
replaces the equality operators for those allocators with inline friends
that support heterogeneous comparisons.  (I'm not changing all ext
allocators because some are bit-rotted already).

Additionally, the equality operators for comparing two std::allocator
objects of the same type are now defined as inline friends. Those
overloads don't need to be declared at namespace scope, because they
aren't specified in the standard (but they're needed in this
implementation to avoid ambiguities caused by the extra overloads
defined for the base allocator type).

	* include/bits/allocator.h
	(operator==(const allocator<_Tp>&, const allocator<_Tp>))
	(operator!=(const allocator<_Tp>&, const allocator<_Tp>)): Replace
	with inline friends.
	* include/ext/debug_allocator.h (operator==, operator!=): Replace
	with inline friend functions that compare to rebound allocators.
	* include/ext/malloc_allocator.h (operator==, operator!=): Likewise.
	* include/ext/new_allocator.h (operator==, operator!=): Likewise.
	* testsuite/ext/debug_allocator/eq.cc: New test.
	* testsuite/ext/ext_pointer/alloc_eq.cc: New test.
	* testsuite/ext/malloc_allocator/eq.cc: New test.
	* testsuite/ext/new_allocator/eq.cc: New test.

From-SVN: r265036