* src/reader.c (grammar_current_rule_check): Also check that $$

is used.
Take the rule to check as argument, hence rename as...
(grammar_rule_check): this.
* src/reader.h, src/reader.c (grammar_rule_begin, grammar_rule_end):
Rename as...
(grammar_rule_begin, grammar_rule_end): these, for consistency.
(grammar_midrule_action, grammar_symbol_append): Now static.
* tests/torture.at (input): Don't rely on the default action
being always performed.
* tests/calc.at: "Set" $$ even when the action is "cut" with
YYERROR or other.
* tests/actions.at (Exotic Dollars): Instead of using unused
values, check that the warning is issued.

tests/calc.at

@@ -129,15 +129,15 @@ exp:
 | exp '^' exp        { $$ = power ($1, $3); }
 | '(' exp ')'        { $$ = $2;             }
 | '(' error ')'      { $$ = 1111;           }
-| '!'                { YYERROR;             }
-| '-' error          { YYERROR;             }
+| '!'                { $$ = 0; YYERROR;     }
+| '-' error          { $$ = 0; YYERROR;     }
 ;
 %%
-/* The input. */
+/* The input.  */
 static FILE *input;
 
 ]AT_LALR1_CC_IF(
-[/* A C++ error reporting function. */
+[/* A C++ error reporting function.  */
 void
 yy::parser::error (const location& l, const std::string& m)
 {