[Bf-codereview] Displace Node (issue 5528108)

[dfelinto at gmail.com]

Reviewers: bf-codereview_blender.org, jbkkavt,

Description:
I had to make it into a Complex node to allow the readEWA to be used.
(the other alternative is to expose readEWA to all node types when dx
and dy are passed as parameter to read).

The result is almost perfect (comparing to trunk). The only problem is a
glitch in the middle:

trunk: http://www.pasteall.org/pic/show.php?id=24506
tile: http://www.pasteall.org/pic/show.php?id=24505

I'm yet to investigate the reason. It may be the readEWA code (which is
also used by the MapUV node, but works fine there).

Please review this at http://codereview.appspot.com/5528108/

Affected files:
   source/blender/compositor/CMakeLists.txt
   source/blender/compositor/intern/COM_Converter.cpp
   source/blender/compositor/nodes/COM_DisplaceNode.cpp
   source/blender/compositor/nodes/COM_DisplaceNode.h
   source/blender/compositor/operations/COM_DisplaceOperation.cpp
   source/blender/compositor/operations/COM_DisplaceOperation.h