Changes component hashing method

The first method was just using bitwise XOR of the string hashes of the
components' type IDs. This could be prone to collisions.
Instead, this method sorts, concatenates, and then hashes the IDs.

src/item.cpp

@@ -8069,19 +8069,19 @@ std::string item::components_to_string() const
 
 uint64_t item::make_component_hash() const
 {
-    // First we need to ensure all the IDs are unique, to ensure we don't XOR identical hashes later.
-    std::set<std::string> id_set;
+    // First we need to sort the IDs so that identical ingredients give identical hashes.
+    std::multiset<std::string> id_set;
     for( const item &it : components ) {
         id_set.insert( it.typeId() );
     }
 
-    uint64_t component_hash = 0;
-    std::hash<std::string> hasher;
+    std::string concatenated_ids;
     for( std::string id : id_set ) {
-        component_hash ^= hasher( id );
+        concatenated_ids += id;
     }
 
-    return component_hash;
+    std::hash<std::string> hasher;
+    return hasher( concatenated_ids );
 }
 
 bool item::needs_processing() const