Merging Shrinkwrap Constraint!

+bvhtree cache (if the derived model doenst gets destroyed then the same BVHtree can be used)
	this was needed to allow shrinkwrap constraint to be usable.

It has been ready for a long time.. but only got merged now, for 2.49.

source/blender/include/butspace.h

@@ -729,6 +729,7 @@ enum {
 	B_CONSTRAINT_ADD_PYTHON,
 	B_CONSTRAINT_ADD_CLAMPTO,
 	B_CONSTRAINT_ADD_TRANSFORM,
+	B_CONSTRAINT_ADD_SHRINKWRAP,
 	B_CONSTRAINT_INF
 };