1) The original() of the file layer should store the correct
   KisDefaultBounds object. That was the exact cause of the bug.

2) KisSafeDocumentLoader should not keep the entire copy of the
   document in memory all the time. Clear the pointer when loaded.

3) Add an kritarc option to enlarge the are available for transform
   mask data fetching outside the image.

   Name: transformMaskOffBoundsReadArea
   Type: qreal

   Default value is 0.5, which means the image is expanded up to half
   its size into each of the four direction.

4) Added a unittest for KisFileLayer