reset turn to 0 before and after each test.

save tests that depend on the global turn variable would fail when being run out of order.
this cause issue #560

src/kernel/save.c

@@ -623,6 +623,7 @@ static void write_owner(struct gamedata *data, region_owner * owner)
     if (owner) {
         faction *f;
         WRITE_INT(data->store, owner->since_turn);
+        if (owner->since_turn >= 0) {
             WRITE_INT(data->store, owner->morale_turn);
             WRITE_INT(data->store, owner->flags);
             f = owner->last_owner;
@@ -630,6 +631,7 @@ static void write_owner(struct gamedata *data, region_owner * owner)
             f = owner->owner;
             write_faction_reference((f && f->_alive) ? f : NULL, data->store);
         }
+    }
     else {
         WRITE_INT(data->store, -1);
     }

src/kernel/save.test.c

@@ -162,7 +162,7 @@ static void test_readwrite_dead_faction_regionowner(CuTest *tc) {
     config_set("rules.region_owners", "1");
     f = test_create_faction(0);
     test_create_unit(f, r = test_create_region(0, 0, 0));
-    region_set_owner(r, f, turn);
+    region_set_owner(r, f, 0);
     destroyfaction(&factions);
     CuAssertTrue(tc, !f->_alive);
     remove_empty_units();

src/tests.c

@@ -161,6 +161,7 @@ void test_log_stderr(int flags) {
 
 static void test_reset(void) {
     int i;
+    turn = 0;
     default_locale = 0;
     free_gamedata();
     free_terrains();