Uniquely identifying loads and shunts from matpower format

[rb004f]

In the matpower paresr, shunts and loads are uniquely identified from 1 to n in line order of the bus table, skipping lines that have no shunt or load values, i.e.

	1	  3	0	    0	    0	0	  1	1.06	0	      0	1	1.06	0.94;
	2	  2	21.7	12.7	0	0	  1	1.045	-4.98	  0	1	1.06	0.94;

the first load is at bus 2 and will be identified with id "1"

Most of the time this is fine, however, this can make using the extended matlab parser to add load or shunt information tricky as this requires knowledge that this is how the numbering is being done and for big files this can be non-trivial.

Given than matpower restricts a single load and single shunt per bus, I might suggest giving the loads and shunts the same id as the bus to make the extended data format easier to support.