In some (weird) cases, the final state number is incorrect.

Reported by Alexandre Duret-Lutz.
* src/LR0.c (state_list_append): Remove the computation of
final_state.
(save_reductions): Do it here.
(get_state): Alpha conversion.
(generate_states): Use a for loop.
* src/gram.h (item_number_is_rule_number)
(item_number_is_symbol_number): New.
* src/state.c: Use assert.
* src/system.h: Include assert.h.
* tests/sets.at (Accept): New.

src/system.h

@@ -52,6 +52,8 @@
 typedef size_t uintptr_t;
 #endif
 
+#include <assert.h>
+
 #include <verify.h>
 #include <xalloc.h>