Keying Screen node from tomato branch

Merge Keying Screen node developed in tomato branch into trunk.

This node is aimed to make dealing with non-even greenscreens better
by generating gradiented image which could be used a input for keyer
nodes.

Based on building voronoi diagram using motion tracking markers as
sites position and average pattern color as color for that site.

Pretty straignforward node, some documentation is there
http://wiki.blender.org/index.php/User:Nazg-gul/Keying#Screen_color

source/blender/compositor/intern/COM_Converter.cpp

@@ -112,6 +112,7 @@
 #include "COM_DoubleEdgeMaskNode.h"
 #include "COM_CropNode.h"
 #include "COM_MaskNode.h"
+#include "COM_KeyingScreenNode.h"
 
 Node *Converter::convert(bNode *bNode)
 {
@@ -351,6 +352,9 @@ case CMP_NODE_OUTPUT_FILE:
 	case CMP_NODE_MASK:
 		node = new MaskNode(bNode);
 		break;
+	case CMP_NODE_KEYINGSCREEN:
+		node = new KeyingScreenNode(bNode);
+		break;
 	/* not inplemented yet */
 	default:
 		node = new MuteNode(bNode);