add_dref_to_list: Internal function to add DrawsRef to a list of DrawsRef objects
Description
Makes sure that DrawsRef with this same index is not already in list.
Although not checked, it is assumed that this is only called on a list
of DrawsRef objects all coming from same model.
Usage
add_dref_to_list(dref, dref_list, sim_dir)
Arguments
- dref
DrawsRef to add
- dref_list
list of DrawsRef objects
- sim_dir
sim@dir