0.8.20.21:

0.8.20.21:
	Add immediate single-floats on x86-64. The implementation is
        conditionalized on (= SB!VM:N-WORD-BITS 64), so the following
        bits need to be done for the 64-bit Alpha port too:

        * Add some new type-test generators (%TEST-FIXNUM-AND-IMMEDIATE,
          %TEST-FIXNUM-IMMEDIATE-AND-HEADERS, %TEST-IMMEDIATE-AND-HEADERS).
        * Modify single-float move-vops and SINGLE-FLOAT-BITS.