Restore conflicting symbol names (CONS, NTH, PRIN1, CDR)

We define BBN-LISP:CONS, etc, and have ELIZA69 use those
instead of CL:CONS, etc.
Protect *readtable*, in case the image is running other programs
Merge commit '48da1bc04595f433c7adf7b4df5c2fa55185b146'