LWG 2441 Provide exact-width atomic typedefs

LWG 2441 Provide exact-width atomic typedefs

	* include/std/atomic (atomic_int8_t, atomic_uint8_t, atomic_int16_t)
	(atomic_uint16_t, atomic_int32_t, atomic_uint32_t, atomic_int64_t)
	(atomic_uint64_t): Define (LWG 2441).
	* testsuite/29_atomics/headers/atomic/std_c++0x_neg.cc: Remove empty
	lines.
	* testsuite/29_atomics/headers/atomic/types_std_c++0x.cc: Test for
	the new types.
	* doc/xml/manual/intro.xml: Document DR 2441 status.

From-SVN: r238534