If conflict resolution makes states unreachable, remove those states,

report rules that are then unused, and don't report conflicts in those
states.
* src/conflicts.c, src/conflicts.h (conflicts_update_state_numbers):
New global function.
* src/lalr.c, src/lalr.h (lalr_update_state_numbers): New global
function.
* src/main.c (main): After conflict resolution, remove the unreachable
states and update all data structures that reference states by number.
* src/state.c (state_new): Initialize each state's reachable member to
false.
(state_mark_reachable_states): New static function.
(state_remove_unreachable_states): New global function.
* src/state.h (struct state): Add member bool reachable.
(state_remove_unreachable_states): Prototype.
* tests/conflicts.at (Unreachable States After Conflict Resolution):
New test case.
* tests/existing.at (GNU pic Grammar): Update test case output now that
an unused rule is discovered.

src/conflicts.h

@@ -23,6 +23,19 @@
 # include "state.h"
 
 void conflicts_solve (void);
+
+/**
+ * Update state numbers recorded in internal arrays such that:
+ *   - \c nstates_old is the old number of states.
+ *   - Where \c i is the old state number, <tt>old_to_new[i]</tt> is either:
+ *     - \c nstates_old if state \c i is removed because it is unreachable.
+ *     - The new state number.
+ *   - The highest new state number is the number of remaining states - 1.
+ *   - The numerical order of the remaining states has not changed.
+ */
+void conflicts_update_state_numbers (state_number old_to_new[],
+                                     state_number nstates_old);
+
 void conflicts_print (void);
 int conflicts_total_count (void);
 void conflicts_output (FILE *out);