[Bf-python] Python functions to call internal boolean operations

[Frédéric COIFFIER]

This patch defines 3 functions to the Object API :
 
 > difference(Object) 
 > union(Object) 
 > intersection(Object)
 
 Thanks to these functions, I can write : 
 
 > newobject = sphere1.difference(box2)
 
 This patch was made against blender 2.41 source code.
 Currently, the code doesn't check if the Object is a mesh. (As I'm really a 
beginner with blender and the blender code, maybe this patch is dirty.)

The patch can be found here :
http://projects.blender.org/tracker/index.php?func=detail&aid=3928&group_id=9&atid=127