Bugfix: Saving in the NBTTag file format is alot faster when compressing the complete data once at the end, instead of consecutively compressing it in many little pieces. The larger the data, the more of a impact this bug has. This issue has become very noticable with the saving of structure files since 1.6.4, mainly because of the file Mineshaft.dat. But it is not limited to the structures. This code is used in many other places throughout the server code as well, which may benefit from this fix