Btrfs: add a sanity test for btrfs_split_item

While looking at somebodys corruption I became completely convinced that
btrfs_split_item was broken, so I wrote this test to verify that it was working
as it was supposed to.  Thankfully it appears to be working as intended, so just
add this test to make sure nobody breaks it in the future.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/super.c

@@ -1789,7 +1789,12 @@ static void btrfs_print_info(void)
 
 static int btrfs_run_sanity_tests(void)
 {
-	return btrfs_test_free_space_cache();
+	int ret;
+
+	ret = btrfs_test_free_space_cache();
+	if (ret)
+		return ret;
+	return btrfs_test_extent_buffer_operations();
 }
 
 static int __init init_btrfs_fs(void)