DO-SYMBOLS: duplicates and shadowings

["Scott E. Fahlman" <Fahlman@CMU-CS-C.ARPA>]

The Spice Lisp system has now been changed by Rob Maclachlan so that
DO-SYMBOLS does the right thing (according to my latest proposal):
inherited symbols are presented, there is no special effort to eliminate
duplicates, and shadowed symbols are eliminated.  As I understand it,
the latter is accomplished by keeping track of which packages contain
*any* shadowed symbols, and for symbols exported by these packages doing
what amounts to a call to FIND-SYMBOL on each candidate.  Rob tells me
that even when this extra checking is being done, it doesn't hurt us too
much in speed.

-- Scott