0.8.21.50:

0.8.21.50:
        * Changed implementation on ALLOCATE-VECTOR on X86:
        ... two VOPs: A-V-ON-HEAP and A-V-ON-STACK;
        ... choice between them is made with LTN-ANALYZEr;
        ... A-V-ON-STACK always fills vector with zeroes (fixes bug
            reported by Brian Downing).