When to creat PURE symbols (sy2blks)

[JONL at MIT-MC (Jon L White)]

Any symbol created by RINTERNing, such as thru READ and FASLOAD
(of course, assuming *PURE = T), and thru PURECOPY, and at no
other times.  Thus the current usage on PNGNK1, PNGNK2 etc by
GENSYM, MAKNAM, READLINE, and COPYSYMBOL will never directly
create symbols with pure structure.