Distinguish the 3 different methods for acquiring pixel color values (executePixel, executePixelSampled, executePixelFiltered).
This makes it easier to keep track of the different sampling methods (and works nicer with IDEs that do code parsing).
Differential Revision: http://developer.blender.org/D7
The issue with wrapping is that it requires correct interpolation of the border pixels. Since interpolation is done at the far left end of the node tree in buffer/image/etc read operations, the wrapping
setting can not be used directly in those operations (otherwise in-line translate operations would cause conflicts). To make wrapping work correctly we need to add a buffer in front of the translate
operation, which can then be interpolated correctly based on wrapping. The WrapOperation becomes a variant of ReadBufferOperation, which uses its wrapping setting to determine the correct "extend" mode
for interpolation of the buffer.
