0.9.8.20:

0.9.8.20:
        Final batch from sbcl-devel "Changes to GENCGC memory zeroing"
	in 2005-12).  Use hand-coded assembly for zeroing memory in
	GENCGC instead of the platform memset/bzero.

        * Use MOVNTDQ on x86-64
        * Use MOVNTDQ on x86 that supports SSE2 (basically Pentium 4 and
          newer)
        * Difference to the version posted on sbcl-devel: Do *not* use
          the MMX MOVNTQ for x86 that supports MMX but not
          SSE2. MOVNTQ apparently had very bad performance on K7
          Athlons/Durons.
        * Use REP STOSL on remaining x86.