end token in rules, %type, %printer, or %destructor

[Joel E. Denny]

If the user declares his own end token (token 0), should Bison allow him 
to put it in a grammar rule?  Currently, it does.

Should Bison allow the user to declare a %type, %printer, and %destructor 
for the end token?  Currently, it does.  However, until we figure out 
whether glr.c really needs to pop the end token twice while yacc.c doesn't 
pop it at all, I think we should disallow these.

For now, I'm planning to prevent the default %printer and %destructor from 
being used for the end token... whether the user declares the end token or 
not.

Joel