* data/glr.c, data/lalr1.cc, data/yacc.c: When YYABORT was

invoked, yydestruct the lookahead.
* tests/calc.at (Calculator $1): Update the expected lengths of
traces: there is an added line for the discarded lookahead.
* doc/bison.texinfo (Destructor Decl): Some rewording.
Define "discarded" symbols.

data/lalr1.cc

@@ -714,6 +714,10 @@ yyacceptlab:
 
   /* Abort.  */
 yyabortlab:
+  /* Free the lookahead. */
+  YY_SYMBOL_PRINT ("Error: discarding lookahead", ilooka_, &value, &location);
+  destruct_ (ilooka_, &value, &location);
+  looka_ = empty_;
   return 1;
 }