Clarification on OWN-SYMBOL

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

Probably most users wont have to do OWN-SYMBOL declarations, since
they will not be concerned with either of the two far-out cases
that cause problems:
1) when a macro definition expects to use, in its body, the renamed
   versions of some system function, which was made into a macro by the user,
2) when the integrity of the compiler is at stake, such as would be the case
   if some simple function was defined as a macro and then the toplevel
   usage of the compiler would be non-standard; or when some simple system
   function is redefined as a SUBR (or LSUBR) and the compiler has not 
   snapped the compiled-code links to the system version.