Gobble, gobble

[Richard L. Bryan <RLB at MIT-MC>]

The current EXTBAS has SI:EXTEND-LENGTH subr defined as
(defun si:extend-length (x) (si:extend-length x))
or something equivalent, expecting a macro definition for si:extend-length
to come in from EXTHUK.  It did, but after that SI:EXTEND-LENGTH was 
own-symbol'ified, leading to a short inner loop on si:extend-length
tail recursing to itself, but not terminating in finite time.

(btw, this is the source of the previous bug I misreported - BIL)