bmesh python api change in internal behavior.

* Only have 1 python object per bmesh, vertex, edge, loop, face.
* Store pointers back to the python data in a custom data layer so as not to use more memory for normal editing operations (when pythons not running).
* Currently this data is created and freed along with the BMesh PyObject.
* Incidentally - this fixes comparisons for bmesh elements which wasnt working before.

source/blender/bmesh/bmesh_class.h

@@ -179,6 +179,8 @@ typedef struct BMesh {
 	ListBase errorstack;
 	struct Object *ob; /* owner object */
 	
+	void *py_handle;
+
 	int opflag; /* current operator flag */
 } BMesh;