fix for asserts added in own recent commit with more strict type-checking

- BMO_slot_copy now only copies compatible elements.

other minor changes
- don't use text.format(...), convention for UI scripts is C style string formatting.
- rename bmo_edgenet_prepare --> bmo_edgenet_prepare_exec
- float/double warning in bevel.

source/blender/bmesh/intern/bmesh_operator_api.h

@@ -136,8 +136,8 @@ typedef enum eBMOpSlotSubType_Ptr {
 } eBMOpSlotSubType_Ptr;
 
 typedef union eBMOpSlotSubType_Union {
-	eBMOpSlotSubType_Map elem;
-	eBMOpSlotSubType_Map ptr;
+	eBMOpSlotSubType_Elem elem;
+	eBMOpSlotSubType_Ptr ptr;
 	eBMOpSlotSubType_Map map;
 } eBMOpSlotSubType_Union;