Compare two DOFObjectID's. 
This can also be used as a comparator function for sorting. 
- Note
 - If both are NULL, they are considered equal. If only one is NULL, it is considered less than the other. 
 
- Parameters
 - 
  
  
 
- Returns
 - Zero if exact match. 
 
- 
Positive value if oid1 > oid2. 
 
- 
Negative value if oid1 < oid2.