detect the case in Core bitvector when the Function Unit says:

detect the case in Core bitvector when the Function Unit says:
"actually, although you said i *could* write to this regfile
(and therefore have been reserving a write hazard protection for me)
actually i'm not going to write to it."

this situation occurs when:
* at issue time a wrflag (from PowerDecoder decode_regspec_write) was HI
* at ALU output time (alu.n.o_ready) the FU dest.data.ok flag is LOW

under these unusual but perfectly valid circumstances the write hazard
bitvector MUST still be cleared