set_parent_refcount
Description:
Sets the parent_refcount field of Structure.
This field is used to determine whether a structure is mutable or not. This function should only be called by code implementing parent objects of Structure, as described in the MT Refcounting section of the design documents.
Parameters:
| this | |
| refcount | 
           a pointer to the parent's refcount  | 
      
Returns:
| 
           true if the parent refcount could be set.  |