Fixes fixSortColumn's Random Inital Sorting

When loading a GridField with several new items without a sort order (e.g. after uploading 10 images via GridFieldBulkEditingTools), it would previously apply a seemingly random order to them. This fix ensures that the order applied is the same order as the items were created (or uploaded) in.
Merge pull request #57 from purplespider/patch-1

Fixes fixSortColumn's Random Initial Sorting