add_prepared_statement
Description:
Declares that prepared_stmt is a prepared statement object associated to gda_stmt within the connection (meaning the 
      connection increments the reference counter of prepared_stmt).
If gda_stmt changes or is destroyed, the the association will be lost and the connection will lose the reference it has on 
        prepared_stmt.
Parameters:
| this | a Connection object | 
| gda_stmt | a Statement object | 
| prepared_stmt | a prepared statement object (as a PStmt object, or more likely a descendant) |