truncating and deleting regular files are unbound operations,
so it's not good to do them in a single transaction. This
patch makes btrfs_truncate and btrfs_delete_inode start a
new transaction after all items in a tree leaf are deleted.
Signed-off-by: NYan Zheng <zheng.yan@oracle.com>
Signed-off-by: NChris Mason <chris.mason@oracle.com>