1.0.4.67: Minor cleanups

1.0.4.67: Minor cleanups

        * Make PCL aware of SB-EXT:MUFFLE-CONDITIONS declaration. Suppresses
          bogus warning when that declaration is used in a method body.
          Reported by Kevin Reid on sbcl-devel 2007-04-09.
        * Fix a typo in a variable declamation, pointed out by Peter Graves.
        * Add some eval-whenage around the DEFCONSTANT for
          +SSET-REHASH-THRESHOLD+, since it's used in the same file inside
          a #.. This should restore building with clisp to the normal
          level of brokenness.