0.8.20.27:

0.8.20.27:
	Fix x86-64 backend bugs found using Paul Dietz's random tester.
        * Sign-extension in constant LOGAND, + and TRUNCATE VOPs.
        * Sign-extension of literal (unsigned-byte 32) passed as
          arguments on the stack.

        Fix handling of :START1 and :START2 in the string comparison
        deftransforms on simple-base-strings (ansi-tests MISC.572/573/574).

        Minor cleanup: Use the already defined *cache-expand-threshold*
        instead of magic numbers in pcl/cache.lisp.