Symbols with precedence but no associativity, and whose precedence is
never used, can be declared with %token instead. The used precedence
relationships are recorded and a warning about useless ones is issued.
* src/conflicts.c (resolve_sr_conflict): Record precedence relation.
* src/symtab.c, src/symtab.h (prec_nodes, init_prec_nodes)
(symgraphlink_new, register_precedence_second_symbol)
(print_precedence_warnings): New.
Record relationships in a graph and warn about useless ones.
* src/main.c (main): Print precedence warnings.
* tests/conflicts.at: New.
In a declaration %token A B, the token A is declared before B, but in %left
A B (or with %precedence or %nonassoc or %right), the token B was declared
before A (tokens were declared in reverse order).
* src/symlist.h, src/symlist.c (symbol_list_append): New.
* src/parse-gram.y: Use it instead of symbol_list_prepend.
* tests/input.at: Adjust expectations.