Always define word-wide CAS for x86 (MS VC++ 8 or later)

Always define word-wide CAS for x86 (MS VC++ 8 or later)

Visual Studio 2005 (MS VC++ 8.0) discontinued support of Windows 95.
This patch deprecates AO_ASSUME_WINDOWS98 macro.

* configure.ac (AO_ASSUME_WINDOWS98): Remove AH template.
* doc/README.txt (AO_ASSUME_WINDOWS98): Remove documentation (as
relates only to Win95).
* doc/README_win32.txt (AO_ASSUME_WINDOWS98): Likwise.
* doc/README_win32.txt (AO_ASSUME_VISTA): Update documentation.
* src/Makefile.msft (CFLAGS): Remove "-D AO_ASSUME_WINDOWS98".
* src/Makefile.msft (test_atomic_w95): Remove target.
* src/Makefile.msft (check): Do not call test_atomic_w95; remove the
corresponding printed message.
* src/atomic_ops/sysdeps/msftc/x86.h: Remove AO_ASSUME_WINDOWS98 from
comment.
* src/atomic_ops/sysdeps/msftc/x86.h (AO_ASSUME_WINDOWS98): Define
(implicitly) if _MSC_VER >= 1400.