/initrd/init decode_spec {P, Z, F, A, Y}DRV & PSAVE

# ln# 897-905 of /initrd/init (tahrpup)
# ln# 958-996 of https://github.com/puppylinux-woof-CE/woof-CE/blob/c96d661c2232caef1d69c693de673fb0e54796f8/initrd-progs/0initrd/init#L958
#100915 technosaurus recommendation (see above)...
[ "$PDRV" ] && { decode_spec "$PDRV"; P_BP_ID="$ONE_BP_ID"; P_BP_FN="$ONE_BP_FN"; PDRV=""; }
[ "$ZDRV" ] && { decode_spec "$ZDRV"; Z_BP_ID="$ONE_BP_ID"; Z_BP_FN="$ONE_BP_FN"; ZDRV=""; }
[ "$FDRV" ] && { decode_spec "$FDRV"; F_BP_ID="$ONE_BP_ID"; F_BP_FN="$ONE_BP_FN"; FDRV=""; }
[ "$ADRV" ] && { decode_spec "$ADRV"; A_BP_ID="$ONE_BP_ID"; A_BP_FN="$ONE_BP_FN"; ADRV=""; }
[ "$YDRV" ] && { decode_spec "$YDRV"; Y_BP_ID="$ONE_BP_ID"; Y_BP_FN="$ONE_BP_FN"; YDRV=""; }
[ "$PSAVE" ] && { decode_spec "$PSAVE"; SAVE_BP_ID="$ONE_BP_ID"; SAVE_BP_FN="$ONE_BP_FN"; }
SAVE_BP_DIR=""
[ "$SAVE_BP_FN" ] && [ "${SAVE_BP_FN:$((${#SAVE_BP_FN} - 1))}" = "/" ] && SAVE_BP_DIR="$SAVE_BP_FN" #last char